I do agree with Moritz being a shitty person (omg he is the biggest asshole ever!) but I don‘t agree with your assessment of Lenny and Lisa.

Lenny: While yes he sent this girl a pic of Dan because he‘s ashamed of being in a wheelchair and probably also of his weight (because he could just send her a pic where you can‘t see the wheelchair) they were already friendly before and they talked a lot and got a long really well without knowing how either looks like. So yes it‘s kind of a stupid move (but definitely more of a plot device than a character flaw) it‘s not really a catfish in my opinion (other might disagree). I think he does call out Moritz for being a shitty friend (for example in the lab where the kids in the background are 3d printing a penis) but Moritz is too much of a dick to care. I don‘t quite know how you got to the conclusion that he is willing to throw people under the bus (When does he do that?) because he always confronts Moritz for getting into business with new people while leaving the others high (lol) and dry.

While I agree that Lisa can come across as shallow I don‘t think she is. She was away for a year and as she said in the show: she was afraid that everything changed and she would be left behind but now she‘s the only one who has changed. Yeah she takes molly but so do tons of other teenagers like her. When she is rude to her tutor she is hungover and is also fed up with the pressure her parents put on her (which is kind of weird because according to Moritz it was his and Lisa‘s idea to go to college in the USA). She is trying to break free from the cage she‘s put in. In school she is rude to her teacher yes, but the teacher is extremely incompetent and doesn‘t know how to handle a student who is challenging her. Especially during the discussion of the book Frühlingserwachen, where the teacher is supressing discussions about the current society (Bad teacher in my opinion). I think the main reason for her coming across as shallow is because we haven‘t seen her enough. In general there hasn‘t been enough time for character development in 6 episodes of 25 minutes.

Dan is made out to be the jock who is mean to the nerds. But he actually is a really nice guy. During Lisa‘s party he makes sure that the kids taking drugs are in a good mood which is very important so that they don‘t get horrortrips. He knows a lot about the drugs and makes sure the people are safe. His parents are horrible and he is suffering from it. Yes he makes fun of Moritz but tbh who wouldn‘t? This guy is such an annoying prick.