This is essentially the same argument that keeps Mega-Gyarados unbanned.so, i'm gonna briefly talk about the problem with an anti-megagross ban that the pro-ban users seem to gloss over; its versatility. realistically, megagross will have mash / ihead and bp almost all the time. they're really necessary moves, and this is supported by 1630 usage stats. so, what about the other two? yes, two. that's the problem; it only gets 2 coverage moves. no, it turns out that you can't run zen headbutt, rock slide, sub, tpunch, ice punch, earthquake, hammer arm, magnet rise, etc all on the same set. you also only get 1 ev spread, believe it or not. yes, this mon is versatile. however, with only 2 coverage slots you're almost always gonna get walled by a ton of pokemon. there aren't too many hard counters, yes, but it's not really as versatile as people make it out to be. even in the case that it was extremely versatile and had almost no counters, look at kyurem. it has the item slot to allow it to run scarf, icium, specs, band and other lure sets to take advantage of its versatility. if that sounds unbeatable, it didn't even get banned. don't rly want to talk about kyub though because that's not what this post is about!
I’ve said it before and I will repeat myself here. Losing to sleep hax or Jirachi is no different from losing to getting crit or missing a move like Hydro Cannon or getting frozen by a move like Ice Beam. It may feel different, but it isn’t.