It doesn't make sense to rule out 'mainstream' as a category. Maybe it depends on what stations you listen to when, but I've definitely heard steppable music.
On an aside, uugh I wish anime wasn't so popular :< a lot of them basically ARE mainstream songs if you look at how they're stepped with like 8ths, 8th jumps to the lyrics, occasional 16th fills and w/e. again not universally bad but I wish they weren't instant mass download material |