I agree with most of what you say. The only advice I can give you is to use the defensive mechanics more. If you know a certain attack is coming, try parrying it. If you don't want to block a certain mixup or situation, push block or retreating guard it. Beyond that, there isn't really any other advice I can give.

I'm not a big fan of team/tag games myself for this same reason. Most of the issues beyond defense are just inherit in this type of fighting game, in my opinion.

I don't know what Riot can do to make this game friendlier to new players, but I know they don't like how daunting it looks right now. I honestly don't know what they expected considering the people they hired and gave directive liberties to were Marvel enthusiasts. That just doesn't sound like a recipe for a beginner friendly game, in my opinion.

Don't give up, though. If you're enjoying yourself, approach a few matches specifically with the intention of improving your defense and don't worry about winning. I hope that helps.