I am not really interested in voting for suspect, but I have played some games on my alt and I have played a lot of games in the metagross meta. I dont know 100% sure if mega metagross should be banned or not since a lot of these arguments are pretty terrible, but I will give my opinion.
Let me talk about meta metagross first. Metagross is really solid mon. Earlier this gen i built a few offensive teams, and because of metagross I had to try some cool mons like t wave klef, defensive lando-t, thundy-i, victini, scarf tran, rotom-w, bisharp, scarf chomp, mega scisor, talonflame and pursuit mega metagross. Almost all my offensive teams had 2 or more of these mons. It wasnt that much of a hassle because I use most of these mons on offense anyway. However they arent a 100% win against mega metagross. Gross is still a huge threat and can easily win if I play to carelessly and puts tons of pressure on my team. Allowing it to get in on anything that can't damage it forces me to bring in my check allowing gross to weaken my check and simply switch out. When facing gross I usually make a lot of double switches, so gross cant just come in and kill something. The only good thing that comes out of gross vs offense match up is that gross almost never runs agility, so you dont have to be scared of that. If it does have agility yeah gl.
I have found balance has an a lot easier time checking mega metagross, because they can afford to use some decent counters. However when building balance I mostly have to use the same team building formula of water for gross and a grass mon. They usually work to take on the notorious core of mega meta + keldeo. This core is great against all playstyles and that is why I run the water and grass core. This could be why hippo+starmie+ferrothorn is such a great core. I have also found that these cores are just solid all around. The only problem is that this can be called as centralization, because it forces you to use this core on balance unless you want to lose. However, there are different variantions of the core, and can be used in many different ways. Without mega metagross I feel like different team archetypes can be used more safely and effectively.
Finally, you have how mega metagross matches vs stall. I have found that stall easily has the best match up against this beast. Common stall cores work well as they take on both mega metagross and cm keldeo, unless you allow your keldeo counter to be weaken or cant break through sub. Stall teams utilizing haze tenta(for laddering most likely), mega venu, amoonguss, slowbro, and slowking do great against keldeo, while counter skarm, quag, gliscor, slowbro, slowking, bronzong, jirachi, defog mega zor, and alomomola all do well against gross. I have found stall to be the best against mega metagross and it doesnt have to worry about it too much. They really just have to worry about it partner in crime keldeo.
I feel like mega metagross is not broken in a traditional since, but more in a unhealthy way. It is not as centralizing as like aegi which made mons unviable, but it makes the meta stale in away in which you have to run the same team archetypes to deal with it, not counting stall. Offense just has a hard time handling it in general with the few checks who do an alright job and balance is pretty much the same team archetype every time. Banning metagross doesnt make anything significantlu better since most fairies could get through mega meta with a fire or ground move. However it does make them a bit better because one of their biggest threats are gone. It doesnt make something like fairy spam a thing though. I am not really sure if mega meta should be banned or not. At first I wanted it gone, but I have come to realize it is not as simple as it sounds. I will probably play more on the suspect ladder in sometime ,because people will have probably have found what works and what doesnt, giving me an idea of what the meta without meta will be like. Thats all I got :3
sorry if there is grammar mistakes on my phone rn