If there are going to be alternative themes, the first job is for them to work! I use Ambiant Dark, but it gets applied patchily. Even default apps, like Firefox, are not rendered properly. It is pathetic, truly. I find myself often squinting to read light grey text on a white background, or black text on a dark grey background, and such utter nonsense.
This is probably the clearest demonstration of why the Linux desktop is going nowhere. After more than two decades it still cannot implement desktop themes properly, such that they get applied uniformly across all apps, or even the default apps.