the way for singers/ musicians to improve is to rehearse and go to workshops etc,.
I can only speak from my own experience,which is generally[ singers at clubs where I have been guesting],and they have all been pretty good recently.
I have strong opinions about people reading words and using crib sheets[although one singer at Robin Hoods Bay ,did give a good rendition while surreptiously using a crib sheet].
nobody is forced to go to a particular club,there are generally choices,so why not let all the shit performers congregate together,and let others go elsewhere[just joking].
seriously,it is up to performers who expect to make money out of clubs to put something back in,one floor spot once a month by competent performers,would go some way to improving standards.