I think several of the arguments/reasoning made for banning (or even watching) certain elements of the meta are misleading or untrue in a lot of ways.
1. Magic Bounce
c) Both player have a bouncer that works, making consistent progress remotely impossible on both sides (we're in a Regenerator / Poison Heal metagame), meaning matchup will inevitably decide the match.
The claim that progress is "remotely impossible" on both sides of a match just because there's magic bounce is completely untrue. With the sheer quantity of offensive threats in the meta, there's more than enough opportunity to pressure opposing teams through the use of pivots, high base power moves, and prediction-based play. Framing competitive play as depending on hazards is an incomplete way to look at any meta--and if any individual finds themselves consistently struggling
just because they can't get up hazards, that points more to a teambuilding/relative understanding of gameplay issue than there being something inherently wrong with the meta.
Next, I think it's utterly unreasonable to talk about "matchup inevitably [deciding a] match" as if matchups don't naturally play a major role in determining advantage/disadvantage states of literally
any team in
any match of any given meta. While it's always possible to either get lucky and/or attempt to outplay an opponent by predicting what they'll do next, it's not as if there's any reliable way to guarantee a win every single time--that simply isn't the nature of pokemon.
Something I do agree with is that while certain core abilities/elements (mbounce, regen, pheal) have stayed the same as they were one or even two generations ago in AAA play, something seems to have changed--especially with the latest round of DLC--that is making it more difficult to deal with the same common threats as we had before. Personally, I'm loathe to ban mbounce solely because in all of the thousands of AAA games I've played/watched this gen, I've seen nothing that has directly pointed to mbounce being such a glaring problem that it suffocates the meta. Certain playstyles/players/team archetypes struggle against magic bounce, but that's just how matchups work. Not being able to just blindly spam hazards is one of the things that makes this tier unique in comparison to standard ones like OU--things aren't meant to be the same. If a hazard-based playstyle wants to be empowered, then it needs to be backed up by hazard setters that can threaten bouncers in some way and/or means to deal with Heavy Duty Boots (which is pretty common right now, I might add).
Aside from all of that, it's also worth noting that more often than not, some of the pokemon that run mbounce are giving up a more defensive ability that potentially opens up holes in their team:
Buzzwole - Okay I think this mon is broken anyway so we won't go into it here
Mandibuzz - While mbounce mandibuzz is certainly powerful (and a bane of ferrothorns everywhere) it's not as if mandibuzz is 255/255/255 bulk. It can still be worn down by pivoting moves or hit with status through secondary effects like any other pokemon since it isn't poison heal; it's still susceptible to high base power neutral attacks; it's especially weak to setup sweepers because it isn't Unaware; it's still weak to supereffective moves because it isn't volt absorb or some other immunity ability <--all of these are some common
and arguably viable ways to make progress against mandibuzz without setting up a single hazard
Mew - Running mbounce on your Mew straight up just means you're forgoing Dauntless Shield (dshield)--and I think I can safely say that anyone who regularly plays AAA knows how amazing the +1 defense from dshield is on any Mew. It makes a world of difference in checking would-be terrifying physical attackers, namely Terrakion, Zygarde, Zeraora, and Mamoswine. Running mbounce means it is no longer able to comfortably switchin to those pokemon's attacks, meaning that everytime it doubles in expecting rocks, it's risking a 2hko. As an example, There's a huge difference between what a burned/knocked off dshield mew can switch into and what a burned/knocked off mbounce mew can switch into
Corviknight/Hippowdon/Chansey - It's the same pattern--while mbounce is certainly
viable on all of these mons, it's not as if they can't be taken advantage of for running that particular ability over other just as good ones. In Corviknight's case, it's giving up a chance to be volt absorb/flash fire/regenerator/literally anything bc corviknight does it all. In Hippowdon's case, it's giving up dshield, which similar to Mew makes it weaker to physical attackers. And when it comes to Chansey, I don't think much explanation is necessary on how good Unaware Chansey is.
What can be concluded from all of this is that there are
plenty of ways to deal with mbounce once you run into it and are aware of its existence, even if only purely because of the way the information game works in matches. Like I said before, I don't think this meta has ever functioned in a setting where outside of mold breaker variants, people were just throwing up hazards willy-nilly without first gathering information about the opposing team--to me, that's part of how competitive games are supposed to go.
Does mbounce make it difficult to set up hazards? For sure
Does that make it broken? Not quite. You have to consider that Heavy Duty Boots are very common and deter hazards on their own, the reasoning above regarding the sacrifices necessary to run it in the first place, and the ability to apply pressure even without getting the hazards up for free.
2. Poison Heal (pheal)
Playing around bulky Poison Heal setup sweepers (Tapu Fini, Zygarde, Snorlax, Suicune, Garchomp, Landorus) is unreasonably hard right now. DLC has given us a TON of Poison Heal abusers, and very few things to deal with them. Being prepared for all of them can mean only one thing : ability manipulation, which can only be done by Mew, Ferrothorn and Toxapex. This ability has already been brought up, but it is right now more problematic than ever.
This is something that seems to be a recurring subject of grievances for people, and understandably so. Everyone can agree that more often than not, poison healers have a unique way of taking chip damage/heavy hits and slowly but steadily recovering their way back to full over the course of a game. I refuse to agree that it's "unreasonably hard" to incorporate counterplay to pheal into teams. Moves like skill swap, gastro acid, worry seed, are passive ways to deal with them--"ability manipulation" in action. If dealing with poison heal setup sweepers, things like Unaware and Haze help to curb their potential. With that in mind, it might seem as though there isn't anything that can be done outside of those options, but let's not forget that the methods to deal with the mons in question are neither new nor niche. Whenever a mon like Tapu Fini or Suicune is placed in a precarious enough position to warrant clicking protect, it creates situations where the opponent can take advantage of options like switching to another mon (either doubling or clicking a pivoting move), clicking an attacking move again, or simply just setting up expecting the reflexive protect. To some people, having to make that kind of prediction based on probabilities might seem "unfair" for the player who isn't utilizing poison heal, but surely any relatively competitive battle has those moments where you have to place your bets on a non-guarantee. With that in mind, it's not as if the switchins to pheal abusers change in any significant way--you still beat things like Snorlax, Garchomp, and Landorous with strong physical walls like Buzzwole, dshield Mew, and the occasional Hippowdon or Skarmory. If that isn't an option, then you can opt for offensive counterplay that outspeeds and kills/threatens them such as Weavile, Noivern, Mamoswine, etc. In the case of Tapu Fini and Suicune, they still get smashed by Haze Toxapex (same as they would in OU or anywhere, really) as well as powerful electric and grass type moves. It's not as if anyone has to build countermeasures into their teams that they wouldn't need to deal with the meta regardless, so I fail to see specifically how and/or why teambuilding would be totally suffocated. Refusing to incorporate easily accessible counters to a threat doesn't make the threat broken--it just makes the team in question lacking.
3.
Buzzwole
I agree that this might be too much for the meta, and my reasoning isn't anything overly elaborate. To put it concisely, between trying to account for Triage, Dshield, Tinted Lens, Mbounce, and MGuard (what?! yeah, I know--but trust me, it works), more often than not teams find themselves having to resort to running their own Buzzwole as a means of countering it. Tinted Lens specifically manages to blow everything in its way to the shadow realm, barr some oddly specific counters (Runerigus? Palossand? Bruh, say it ain't so), and Triage offers speed control without necessitating a scarf or explicitly speedy mon. Let's also not forget that it still has bug stab, which makes it even more difficult to counter it with something like Mew, which blanket checks a lot of physical attackers singlehandedly. Buzzwole is a tough one to handle for sure.
4.
Tinted Lens
While it's true that tinted lens definitely enables certain breakers to overwhelm would-be counters, I feel it's definitely a bit much to say that there are numerous abusers. Who specifically does that refer to? In my experience, there have only been a few
notably powerful tinted lens abusers, and one of them is Buzzwole the Broken and Busted
who probably needs a ban for several other reasons anyway. Other than that, I can't honestly say that there is some unbeatable listing of tinted lens abusers that rip through teams unabated--if there is, then I'd be happy to discuss them.
5. Zeraora
We'll see.
6. Blacephalon
I have mixed feelings about Blacephalon, to be honest. On one hand it's certified canceraids because of how powerful fire/ghost stab + 150 bp Mind Blown is, coupled with potential trick, knock off, or explosion shenanigans. On the other, it's not the easiest mon in the world to build with, and more often than not it can find itself legitimately struggling to deal with common defensive mons like Tapu Fini, even with minimal investment. I'm open to discussion of blace as a powerful threat, but until further notice I'm hesitant to see it as potentially bannable.
7. Zygarde
In summation: Thousand Arrows + Dragon Tail is aids--let's not even go into cb adapt and pheal. That said, Zygarde's in a weird spot where It might be broken but also does have some reliable counterplay that generally keeps it in check.
I made this post mostly to clarify that exaggerating the severity of certain threats makes it really difficult to pinpoint exactly what's problematic, and generally misleads the less informed by painting a picture that might not all be representative of what the meta is actually like in practice. As always, everything is open to discussion--but we can't just ban every viable ability/mon on a whim outright, so keep that in mind.
and to a lesser extent : 
and to a lesser extent : 
(dshield) 
elec or steel)
ACCURACY
I'm not sure if it does enough over Adaptability or Sheer Force (or Triage or Poison Heal or whatever) to be worth it, but Hyper Voice ignoring Subs is nice.
Kyogre
Groudon
Rayquaza
Lugia
Ho-Oh
Regigigas
Palkia
Dialga
Giratina
Xerneas
Yveltal
Dragonite
Pheromosa
Kartana
Zygarde
Dragapult
Magearna
Zeraora
(ban)
(watch)
(watch)