How to tell a friend that they are the problem?

I know of a person who often rants in the server I am in about how every group he joins is terrible but from what he tells me he usually plays a homebrew class,has a backstory far different than other players(He also insists he is original and other players are unoriginal but the other players think his character is unoriginal. ) The last homebrew class he played was a gunslinger that also deals with demons.

I can tell that he is genuine in his complaints but I believe that he is the problem. I feel like I should tell him but I am not sure how to do it without starting a fight or getting ignored. So my question is how should I do it?