That's exactly the problem, those songs are not in either artist's genre. The artists don't sound similar, but the songs do. By "genre" I mean the effective genre (mood/vibe, instrumentation, pacing, chord progression, etc) of the song, not the nominal genre of the artist.
I would listen to those two songs in a row and be completely satisfied by the transition.
I was a huge Smashing Pumpkins fan when I was young, I'm a big Aphex Twin/Richard D. James fan and I don't know if I'd ever connect those two songs on a playlist or even play them together. That might be the issue, it's too much a subjective judgment.
I've worked and interviewed for companies that do music analysis to find moods, atmospheres, similar timbres, chords and structure to mix and match automated playlists for business needs (restaurants, cafés, retail stores and so on), would like to see what kind of similarity scores they could get between the songs you mentioned.
I would listen to those two songs in a row and be completely satisfied by the transition.