I've only around for a few months, but if I may spread my opinion of on the mega sableye issue. I don't run dark or ghost hardly at all (I haven't even built a mono dark team before, and my ghost team is definitely pathetic), but I am against the ban. At least on ghost, I don't really see dark enough to tell. The only tournaments on showdown do occasionally give me access to players that are several times better than me, and from them and my part of the latter there are two pokemon that (I'm sure there are more, but two I'll talk about) function very similarly to mega sab in my opinion.
The first is snorlax. Specifically, my snorlax, the set I use on my normal team which I currently view as my main. Sab and lax both function as walls. I generally understand a wall to be something that does two things: 1. takes hits without dying 2. slowly kill things or slowly prepare to kill things very quickly. sab uses calm mind to perform the latter part of the second walling point. my lax does the exact same thing using curse. Where sab has wilo-wisp to reduce damage from physical attackers, I have Amnesia on lax to the same thing with special attackers. I typically then see recover on sab (the analog to lax's rest), but it can have a couple different useful moves in place of that or even wilo-wisp. They both then have a single attacking move: sab with dazzling gleam for coverage, and I run last resort because you can't argue with +6 attack last resort... unless your immune. So, sab would currently beat my lax one to one, but I can and have run a different attack to hit ghost types with. In that case I feel like lax would win hands down (I could be wrong). I just decided that the rest of my team could take on ghost, and snorlax just could dish out incredible damage to what he could hit. The main difference between the two is that snorlax doesn't have magic bounce. Magic bounce means you can't really taunt sableye which ruins lax. If hit with taunt before I setup, I literally can't do anything except switch or run down pp on last resort. So, Magic bounce probably make sab a little better at it's job than lax.
The second is Espeon. I don't use psychic and am not too familiar with espeon, but it seems to typically come equipped with calm mind and stored power. I think it can learn wish and probably then has protect, but I'm not certain. It is less of a wall than my lax and sab as it doesn't seem to have a good answer to physical threats (by itself), but stored power is a special attack that has increasing base power with it's stat boost. Add the base power and special attack increase together and you get a great sweep attack. All while increasing it's ability as a special wall. And like sab, espeon has magic bounce, so you can't taunt it to prevent setup. Espeon is lacking in the area of immunities, and stored power is a psychic move meaning dark is immune to it. This means sableye would again win a one to one match up, but espeon has to have a good cover move against dark. If nothing else, any good psychic team will have an answer to dark types; gallade and gardevoir (mega or not) both seem to fill this role very well.
I point those two out because the main complaint to mega-sableye seems to be that the fact that people build counters or checks to just it means he's disturbing the meta in ways that it shouldn't. But sab is not the only one. He just seems to be the most abused and possibly best one, and I'm of the opinion that he's not that much better. Snorlax and Espeon obvious don't disturb the meta to the point of being banned, and I don't see why you would think sableye does just because he is a little bit better at what they all do.
In response to Narset about the boosting physical attacker thing. Should every team run a boosting attacker? Probably, either physical or special if not both, there are threats from both sides. Should every team have an attacker that deals at least neutral damage to sableye? Definitely, users should be trying to build teams that can dish out at least neutral damage to anything that's thrown at them. If someone or several people choose to compound those two to deal with the likes of sableye, so be it.
Mega sableye is annoying, but so is the choice scarf. Annoying is not a good reason to ban something, and that's currently the only one I see being brought up against sableye. Sab is annoying to deal with for some teams just like some types are annoying for other type to deal with as a whole.
Sorry, but I disagree with you. Snorlax does have a neat looking set, but chances are they will only lose one Pokemon to Last Resort, then switch to their ghost type (fire has chandy, water jelli, Grass trev/gourgeist, dark sableye, steel sometimes uses doublade, etc.) and steel/rock resist it and most are naturally bulky. Also, it needs to set up to be a threat, and it can be outsped by stuff. It also hates physical fighting moves before it sets up a few curses. Also, Last Resort is sorta gimmicky, as you need to use all of your moves, and sometimes Snorlax can't tank 3 hits. The factthat it is completely walled by one type (and almost completely walled by 2 others) makes it sorta unviable in mono where every type is usable (even if ghost is used less than most teams). The turns it rests on make it set up bait, as something can set up twice then kill it on the turn it wakes up. It also doesn't have access to 2 of the best abilities in the game in prankster and magic bounce, meaning it can be taunted, phased, and statused (I know rest cures it, but burns make last resort do less, and the chip damage could kill it). It can also be encored into one of its set up moves by shuckle/whimsicott. Sableye on the other hand, cripples physical attackers and sets up, all with priority. Then it can Mega Evolve, become immune to phasing moves/status/taunt/encore, and proceed to sweep with a STAB with no immunities. It also can't be choice tricked, while Snorlax is absolutely wrecked by choice items, rendering it completely unable to do anything except struggle. So, while my tired mind is considering this I have found many ways to efficiently counter Snorlax: Whimsicott, Ferrothorn, every ghost type ever, taunt, trick, encore, whirlwind/roar, hitting it with a fighting move before it sets up (preferably physical, but special would work too, as it needs to set up to wall stuff), and it doesn't have the best support on normal. Sure it gets Heal Bell/Wish support, but normal teams are generally stally, and so doesn't get the offensive support Mega Sableye gets. Mega Sableye on the other hand, is only efficiently walled by Umbreon, and maybe Gardevoir too (but Garde must get burned for synchronize to work), as well as other set up sweepers if you bring it in before they are eliminated (such as Volcarona, Azumarill, Mega Diancie, Zard X, etc.) but Sableye has teammates that can handle all of these (Mandibuzz/tyranitar/Bisharp) allowing it to sit back, then come in and sweep late game once it's threats are eliminated. So, I would say that yes, there is a huge difference between Mega Sableye and Snorlax, especially the Snorlax set you posted. While I can see how it can be amazing, it is walled by so many common Pokemon/moves, including a whole type, and pretty much 2 others.
Espeon is once again walled by a whole type, and has no way to deal with strong physical attacks. Bisharp walls that set so hard its not even funny, can get a SD while you switch, and wreck at least a couple of Pokemon before it dies, or possibly sweep the whole team with Knock Off/Sucker Punch. Btw, it does get wish and protect, and it took me about 12 seconds to figure that out (Google ftw). Yes it gets Magic Bounce but there is a better way to use that: as a supporter. Being immune to taunt/defog/encore is what gives it its main niche: a fast screens setter. With light clay/magic bounce/light screen/reflect/Wish/protect, it is a tremendous supporting pokemon that avoids hazards being set (if you predict right) prevents screens from being defogged, and provides wish support to teammates. If you want a Calm Mind/Stored Power user, use Mega Latias imo, as it is bulkier and has unimmune STAB coverage, with excellent other options for coverage and many viable sets, making it unpredictable.
To conclude, Snorlax and Espeon are nowhere near as good as Mega Sableye, as they lack both priority setup/crippling, and a way to deal with strong physical attacks before they set up (and Espeon never has a way). They also lack a STAB with no immunities, meaning they are completely walled by a certain type, and struggle against others, no matter how much they boost. These Pokemon can be effective, but the sets you posted are gimmicky and sorta niche. I know I sound really harsh (probably anyway), and I'm sorry, but Mega Sableye is much better than these Pokemon and is possibly the most broken Pokemon in mono right now (especially on dark). And, like I said earlier, Snorlax is rekted by loads of status moves, including taunt, trick, encore, etc. Also, a couple things I forgot to mention, Snorlax can also be worn down through Leech Seedl, and Sableye also has 3 immunities and only 1 weakness and 1 resistance, as compared to 1 immunity, and 1 weakness and 0 resistances (Snorlax) or 0 immunities, 3 weaknesses, and 2 resistances (Espeon). Plain typing for these two also doesn't really help their monotypes--they are weak to the same moves as their teammates, while Sableye has tremendous typing. So, Mega Sableye is a lot better at what it does than Espeon/Snorlax and these aren't valid comparisons, especially as those aren't even their most common sets (or their best sets imo).
EDIT: Gdi
Gnief Fiar with snipes <.<