I don't believe in the point of having something being common on teams, that it should be banned. If its common, and its more importantly dominating the meta, there is a definite problem. Such as there's point in not using it, in the case of broken megas in the past, such as M-Luke, M-Kang, but I just bring that up as a case when a new broken mon arises. Thankfully(Fu gamefreak), there aren't really any mons that dominated the metas such as those anymore. But if a pokemon, say, Hippowdon on Ground, or Skarmory on Steel, that is just insanely good on the type and gives insane support to the other members of the team in various ways, they aren't really broken. They are just good mons that warrant usage because they're good in the type and in the meta in general. I don't your example is really that good for this reason, near the end.I hate to bring this up again, but this is a point that I need to get across to people as these people are potential voters in a sablenite suspect test:
Do not cite team support as the sole reason Mega-Sableye should be banned.
Team support is definitely a factor in how good a pokemon can perform, this is true. However, this is akin to saying "it doesn't matter if you pack a Weavile to counter my DD Dragonite; I will simply switch out to Skarmory and your counter means nothing".
I have seen multiple times that people claim that Mega-Sableye makes the matchup lopsided vs. poison teams; this is simply not true. Tentacruel is an excellent answer to the CM set (and if it's a restalk set, it is a hard counter and switches in every time to force out mega-sableye; which btw is not overcentralizing as this also shuts down many stally mons that can be found on many different teams). The utility set is a little harder to deal with, but it struggles to break past Mega-Venusaur / Weezing, and don't forget that poison attacking moves will eventually poison Mega-Sableye through Magic Bounce, assuming that you haven't scald-burned it yet).
I will repeat this in case you missed it; RestTalk Tentacruel is right up there with Volcarona in terms of an excellent mega-sab answer. Obviously Tenta is beaten by Bisharp / Aegislash and friends, but you can say the same for Volc vs. Chandelure / Tyranitar, and nobody is discounting Volc as an excellent answer to Mega-Sableye.
The team support argument, if cited as the main reason it is banned (if it's banned) will lead the Monotype Metagame down a very slippery slope. All of a sudden, Mega-Scizor is too stronk against Rock/Ice/Fairy since hey, it has 5 teammates to rely on in case the rock/ice/fairy player has something that beats it. Let's ban Mega-Scizor!
Or, Lando-I is too strong vs. poison/electric/rock/steel/fire types, and even though I can pack HPice Gengar / Kabutops / w/e, it doesn't matter since I can switch out to my Skarm/Gastrodon/Gyarados. Therefore, team support makes Lando-I too good for monotype, and is overcentralizing; let's ban it!
.... I hope Monotype does not make this mistake. If Mega-Sableye is really such an over-centralizing mon that it takes at least 2 pokemon to not auto-lose to it, then I will accept it when it gets banned. In my experience battling (vs. both n00bs and battlers who know what they're doing), this is not the case.
One final point I'd like to bring up, is that just because a pokemon is good enough to be seen on 99% of teams of that type, does not mean it is overcentralizing. Heatran is found on 99.99% of fire and steel teams today, and requires 1-3 pokemon to check it on ice/grass/steel/bug teams and is more unpredictable than Mega-Sableye (with excellent team support on Steel). Yet nobody is crying for Heatran to get banned...
But let's be real here, there is not much drawbacks to using Mega Eye over any other Dark mega. Other megas do not provide the sheer utility and bulk of M-Eye, and the only one that comes close is Tyranitar-M, and it is worn down by passive damage over time anyhow. Anyhow, team support is a real reason some pokemon get banned. Think back to Char X and why it was banned, not because of how strong it was alone. Incredibly strong, but defensive team support from pokemon like Skarmory, and offensive support like Lando-I broke cores down for it to finish. So I don't think not citing team support is not a good thing. I think team support can be cited for a reason mons get banned. Referring back to early XY, DeoSharp was an insanely powerful hazard stacking core that dominated the metagame of OU. the pokemon that provided that broken support was suspected and banned from the tier to make it more balanced. M-Eye gives potentially broken support in some matchups, therefore I think it can be cited then.
Just my thoughts anyways.