I was going to make this post after I finished getting 2700 COIL but I saw your post and... you hit the nail clean on the head. A lot of us are tired of walking in a mindless circle that degenerates the metagame.
I have a question not just for you, but for a lot of people who are making the same claim that this post makes: What do you mean by degenerates the metagame? I know of a lot of people (myself included) who felt like the bans that were made led us to a very enjoyable metagame at the end of xy. The ladder wasn't centralized around any really overbearing threat(s) [I deal with this later], but there was still some form of order and you had an idea of what to expect (ie: variety but not chaos). Or at least thats how I found it, I honestly want to know how you find this degenerative? Or at least what you mean by that word. (Examples would be nice).
There will ALWAYS be a Pokemon that is as powerful as MegaGross in any given meta.
Now I don't want to say that this is completely wrong, but this is completely wrong. When Mawilite was banned, did some other pokemon randomly start hitting virtually the entire tier for >70% damage unboosted? When Greninja was banned, did we suddenly see pokemon demolishing virtually any defensive core? There will always be top-tier threats, thats how the game works, but (and correct me if I'm wrong) there won't be anything AS powerful as MegaGross. And thats the problem. Toe-to-toe, so many pokemon come up on the short end of the stick vs metagross which gives it time to bash virtually any switch-in quite hard.
This is why Pokemon are categorized by viability. You can ban them, but then a new threat comes into the picture to be suspected. Then you ban that, and the process repeats itself over and over and over until there is NOTHING left. Stopping this ban is actually crucial to breaking a vicious cycle and progessing the state of the metagame.
This may be based on your earlier claim that there will always be a pokemon as powerful as MegaGross, but I'm going to treat it differently. A new 'broken' threat doesn't have to come into the picture at the end of the day. You may end up with some really good top-tier threats, but ones that are manageable. Look at the S-Ranked threats at the end of XY: Charizard X, Greninja, Keldeo, Latios. All of these pokemon have reliable switch-ins that will can counter/check every (reasonable) set. Slowbro, Celebi and Mega Venusaur will (again reasonably) always beat Keldeo. Charizard X had Landorus-T, Slowbro and Hippowdon, Latios had Clefable, Heatran, and Sylveon that could switch in, and Greninja was probably the most broken but guess what? AV Azumarill, Clefable, Ferrothorn (most of the time), and Chansey were safe switch-ins. There are obviously more switch-ins, but those are the ones off the top of my head. So unless you can (a) explain to me how we could have achieved this metagame without banning all those things like Mawile and Aegislash or (b) show me that this wasn't a desireable metagame, then I'm going to stick to my guns and say that XY was indeed a desirable metagame, and since Metagross takes these S-Ranked threats and makes them look like walks in the park, it needs to go.
The suspect ladder itself is proven quite well that you are VERY limited in team building. You are more so limited than you are with Metagross in the tier. Why? because the suspect ladder's dominant mega's can hit a majority of the mega's in this tier for super-effective damage. Which means you are restricting team-building. You are promoting the same over-centralization that people are crying that Metagross causes. Meanwhile the pre-Suspect Ladder had a wide variety of usage, you didn't just have one archetype raining over all. It was used, but it wasn't the only solution.
What proof do you have for that first claim? Or the claim that we're promoting overcentralization? Because in the 60 or so battles I've had on the suspect ladder, I've seen a lot of balance, quite a few HO teams, a handful of weather teams, and maybe 10 or so stall teams. This doesn't seem centralized or restricted to me. Diancie isn't on every team like you make it seem it is, and Fairys didn't suddenly become insanely OP like some people are making it out to be.
And lastly
I'm roughly 700 COIL away from hitting my 2700 so I can attempt to stop this mistake from happening. When the day comes I will be voting no ban, and while I understand a few diehards won't consider changing their mind, I hope that other people, reasonable people, can actually think about this.
I'm not going to get into the rhetoric of that sentence, but I hope you can believe I spent a lot of time thinking about that, and I still disagree.
EDITS: Made the words sound prettier/more technically correct and fixed some grammar issues. (Also added tldr).
TL;DR since this is a long post that hits a lot of points: Please stop making claims without any supporting evidence because they hold as much water as I do saying I'm 7'3" and French. If you say "Banning things degenerates the metagame" please do us all a favor and explain HOW banning this has this effect, and (please for the love of God) provide actual examples. Same thing goes for people claiming that late XY was a terrible metagame. It actually gives us something to debate about/discuss and makes YOUR arguments stronger.