“I began to write fiction on the assumption that the true enemies of the novel were plot, character, setting and theme.” — John Hawkes
I agree with Hawkes. Literature, especially as taught in Junior High English classes, is too important to insist on those archaic unities. Plots went out with I Love Lucy where Desiderio Arnaz clearly demonstrated that there were only three plots known to man, the rest being variations masking as variety. Character is hard to avoid but the classic importance of character development is easy to forget (no, you do not need to identify or fall in love with one of the characters). Setting is only important when the writer needs to bolster his narrative with a setting which evokes themes he (or she) is incapable of evoking himself. Do we need themes? Not really. I suspect the development of thematic fiction was good but it risked falling easily into didactic fiction and that is bad.
I might say that everything is thematic: the boy and girl theme, the levels of fiction theme, the remembrance of things past theme, the talking dog at the end of the world theme. The problem with themes is that they, like plots, get repeated a lot and no amount of variation hides a tired old theme.