The biggest problem is:
People want to get good at team games by playing team games
But the way to get good is through playing 1v1s with conscious effort directed towards analyzing replays and taking feedback from better players, especially (if you can get it) feedback from top players
How do we create a team game environment that teaches people how to get good at team games? Probably, we can't. Maybe we need Rimworld-style tutorials that assess what is going on in the player's game in order to offer targeted advice as the game goes on. So the game would point out basically "hey dude, your economy is grossly unbalanced" or "bro, you're power stalling and you're not taking this reclaim in front of you" or "don't put storages on t1 mexes" or "you shouldn't put pgens around more than 2 of your t1 mexes" "this e storage thing you're doing is abominated" etc.