Nope. The tiny tourney also had them banned and that wasn't just Alola Dex.
I don't know off the top of my head what's eligible for that competition with a Mega, though my guess is it's like three Pokemon and it's a balance/not enough legal Stones thing
You're missing my point. They don't introduce mega evolutions as a means to balance the game. They introduce mega evolutions for marketing, and then after designing them try to figure out stats and ability and stuff that keeps them somewhat balanced. Of course the game isn't balanced, it has over 800 pokémon and that's pretty much impossible to balance, let alone for different kinds of formats (4v4 doubles, 6v6 doubles, 3v3 singles, 6v6 singles, and so on). My point is that they're not going to go through the trouble of making freaking Corsola mega evolve because nobody cares about Corsola.
I'm not advocating to Mega Evolve Corsola
I'm advocating for the existing Megas to be less gamebreaking
yeah, I know there's a lot of Pokemon, and I don't expect all of them to feasible to use, but I expect diverse teambuilding to not be actively hindered by obviously unbalanced mechanics, and try as they may to keep them somewhat balanced, their hands are kind of tied based on the nature of the mechanic
And by letting already very powerful pokémon mega evolve you create a big power creep, which has the main problem that everything else gets lagged behind. Mega evolution overall has primarily been more detrimental to balance rather than boosting it in my opinion, especially Salamence and Lucario.
this is what my concern here is; I'm glad you agree