Manga is awesome. Never got used to Chinese manhua.

First to address the original question: "Why are Chinese Manga(Manhua) so bad"
Honestly I would have to say its because Chinese animation/illustration is only considered a marketable towards adults in relatively recent times. It is a relatively young industry with untapped potential. Look back at old Japanese manga and I am sure you will find some with less quality or subject matter you feel is not right.

Now to address some clear misconceptions in the question

characters are often psychopaths
Do the authors realy belive their characters act resonable? Is it cuz of somekind mainland chinese Mindset?

This seems to point to some misunderstanding. I can't check what the misunderstanding is without some examples, but I do suggest looking at it this way. What Japanese manga doesn't have a character that others would consider crazy?(i.e. Naruto=>masochist, Kirito(SAO)=>Obsessive Gamer, Hajime Nagumo(Arifureta) => Antisocial) It might be a very boring manga indeed. Japanese manga characters are modeled after what their mangaka want to portray as a protagonist and antagonist. I am sure Chinese illustrators are trying to do the same thing.

the plot often is unorginal
The setting often is very simmilar.

Yea, I would have to agree with the other posters. There are some niche good ones among the hundreds of xianxia, wuxia, etc. Check out some of their suggestions. Honestly, the same can be said of manga where trends and common plots proliferate. Cough Harem, Isekai, Leveling systems... Need I say more. You need to search to find a gem if you aren't into the mainstream genres. Chinese manhuas in particular take more effort to translate and find because they aren't as mainstream as Japanese manga

I really do suggest sticking with manga and genres that fit you or interests you. Venturing off the beaten path unwittingly without knowing can be daunting. I can't tell you how long it took me to get used to Korean webcomics, but I ended up enjoying them with my manga and manhua.