I don't know the minimum level you need to not just lose the game but should not be too hard to reach. I'm also not arguing about the mechanics of the fight, there are a lot of them and it is hard.
Tanks: No idea why they hit hard. They also have a finisher if someone is bleeding, its kinda similar to Vix. Sam has the same debuff. No idea why they heal. Also your full team can taunt.
Healer: Their attacks getting stronger the more they use it. Your team can also heal and revive.
Drainers: The buff only happens when someone on their side gets low enough. Did you read some of what I typed before? I brought that up already.
Structures I kinda agree with you on. They can be really annoying to deal with and make fights unwinnable. If I couldn't run from those fights I would fully agree with you.
I also agree about overclock. To my knowledge it also only shows up on Red Bot (which I run from) and the factory (which is optional).
The stealing, I have no clue why they added that but I think they can't steal what you have equipped until you're bag is empty. And yeah common items are not too useful.
Because you are fighting strong enough enemies to get xp that's worth something. Are you draining enemies? Also what tone of voice do you use in you head when reading what I type because I think there is some hostility that is one way. These are genuine questions.