Imagine a wall. It looks like someone shot paintballs at it with extensive splatter. As you draw nearer, however, you can see that it's really a plot. Where the paintballs apparently hit are where a lot of dots landed -- based on the criteria for genre -- which define the genre. The sensible genre arguments are about what the criteria that are plotted[note](and how do you plot all the genre criteria in two dimensions? Talent, my dear, pure talent)and how far out you draw the circle about the "splatter" to demarcate that which is in the genre and that which is not.
Been thinking about it and the superhero genre and the splotches on the wall that come the closest. And what the distinguishing tropes are. As in, the center of the paintball-ish splotch.
Urban fantasy has its points. So do alternate magiteck universes like Operation Chaos and Magic, Inc. (with steampunk nodding in as an earlier version or possibly with just different tech). Space opera, too, but it's the clearest: not only do its wonders need a SF handwave, it needs to involve space, which is not mandatory for the others, and possibly not possible in urban fantasy. The urban fantasy needs the masquerade, with magic and marvels hidden from public eye, and with at least a guiding principle for its marvels, even if it's folklore in general as fed through Hollywood. Steampunk and magiteck also require such a guiding principle with how the magic is ordered and worked into the technology -- even if, in steampunk, it's "not at all."
The reflections led me to the conclusion that the hallmarks of it are the open superpowers, the variegated origins, and the funny costumes and codenames. The fun part is that those last two are among the tropes hardest to justify in-universe. Out of universe, you can see a lot of reasons for them, but in universe is funnier.