You guys keep trying to solve the wrong problem.
Single decks are not the problem, never have been.
Single cards CAN be a problem.. and have been.
However, the staleness and shittyness you run in to is typically just fatigue. Meta fatigue. Netdecking. Lack of strategy and forethought.
The ladder system is stupid. It's the dumbest system to exist in this game.
You need to inject THINKING into the game, if you want to rank up and win then you're going to netdeck and the only thought you have is "which deck has the highest win rate vs the current decks i'm seeing".
That's it.
Tournaments, or even an advanced ladder system that has rounds and deck bans could go a long way.
Like "Bring 3 decks, Ban 1, Bo1".
So you see 3 opponent decks, you can ban 1 out, then you each choose 1 deck of the remaining 2.. you still only play 1 match so as to not be heavily invested (time-wise), but now you've injected some serious strategy into the game.
I'm hesitant to believe the meta is all that shitty right now. Pre-nerfs was worse. This is decent. But we're in the "lull" period of the game. Pros don't care anymore because it's "off-season", so deck innovations are lax, and casuals that netdeck witness this, and also just meta-fatigue due to it being month (3?), already.