That element is Gothitelle / Gothorita. There have been many complaints around its effect on the metagame, crippling defensive teams to the point that they require excessive preparation just on the chance that someone brings these Pokemon to the match, or ignore preparation and simply lose when coming across them. Why Gothorita as well? With Eviolite, its bulk is so similar to Gothitelle that removing one leaves the problem unaddressed. They ruin the viability of would-be good additions to the metagame, and does so in a manner that lacks ideal counterplay as would be fitting for a balanced metagame with player interaction between both players. The removal of this element improves the overall look of the tier as defensive checks to Ubers' powerhouses grow in viability. It improves the spectator point of view as they no longer have to watch a Pokemon simply drain PP without much skill expression from either player. This most importantly helps to balance the metagame and gain a true assessment of Pokemon that could be seen as an overwhelming problem.
So that's how I currently stand. What about the rest of the community?
Personally I think the threat of Gothitelle is somewhat overblown. The problem is that it simply isn't used enough to be a considerable threat in teambuilding, although one thing I will agree with you on is that some teams, notably Stall ones, may just lose at team selection with Gothitelle. But other than Stall, there's hardly anything at all that Gothitelle can really switch in on because Ubers is and always has been a predominantly high offensive metagame. Even the more passive Pokemon like support Arceus forms can still leave a dent with Judgment and Gothitelle must always watch out for Z-Move variants of Arceus. Because of the small selection of Pokemon that Gothitelle can actually check and the fact that Gothitelle is easily revenge killed, I don't think it's presence is enough to be banworthy. As for Gothorita, I've never actually seen Gothorita even once but even though I've been
in Top 500 with a Stall team multiple times during the SM/USUM meta. I believe Gothorita may be super niche and will only be used if Gothitelle gets banned, similar to how Diglett got used in SM OU when Dugtrio got banned.
But to be short and concise, Gothitelle checks a very niche amount of threats and while it's super good at doing it, it's slow Speed and middling physical Defense leaves it vulnerable to being revenge killed. Because of the high offensive nature of the Ubers meta, it's usage has been very low and even when it's used, there's no guarantee Gothitelle will be of any use because of the small amount of threats it can actually check, which is mostly limited to Support Arceus forms. Even most passive Pokemon have a way of checking Gothitelle. Blissey has Shed Shell. Lugia has Whirlwind for the Calm Mind sets. Deoxys-S has Taunt (assuming Deoxys-S isn't fainted in the first three turns). Giratina has Dragon Tail and can't be trapped to begin with. Gothitelle doesn't like taking Sunsteel Strikes from support Dusk Manes. Ferrothorn can beat a Calm Mind set using Leech Seed and Power Whip but is one of the few that's beaten by the PP Stall set. Anything else is just too low of usage or runs Shed Shell (e.g. Toxapex).
If you are implying you want STAG to be banned, then I'm personally uncertain about that. Mega Gengar is in no way overpowered and isn't even the most used Mega Evolution at the top of the ladder, being superceded by Mega Lucario and Mega Salamence at the top of the Ubers ladder. This is straight from the usage data. Mega Gengar is somewhat frail on it's physical Defense and it takes a turn to Mega Evolve which you can switch into a Gengar check and possibly even gain momentum by setting up.
It's difficult for me to say what is and isn't broken without a biased point of view, but I would still like to give my opinion regardless. I honestly think Geomancy is definitely one problem with the meta. It forces people to run a counter to it and because of it, Necrozma Dusk Mane ends up being splashed on every team in an attempt to counter it. People are also talking about banning Primal Groudon. Problem is, if you ban Primal Groudon, you must ban Primal Kyogre too, as even though many people complain about Primal Groudon, Primal Kyogre has a stunningly low amount of actual counters, Primal Groudon and Ferrothorn being the only ones I can actually think of. I suppose I can agree with Solganium Z being banned as it might be too significant of a threat on Double Dance teams.
Other than that, I'm actually uncertain what we could do with the meta. I think Dusk Mane is just too important of a Pokemon to get rid of and Ultra Necrozma is a legitimately healthy addition to the meta. Dusk Mane serves as a Xerneas counter, which more viable Steel types have long been needed, and Dusk Mane serves as the only Steel type that's not countered by Primal Groudon if it holds Ultranecrozium Z. Ultra Necrozma also gets a few other notable Pokemon like Rayquaza and Zygarde-C.