Interesting, I tried a few songs and artist combinations:
I picked a Three 6 Mafia song I used to listen to in my younger years, the particular song I chose has everything in the soundtrack from high hats, to trumpets, several rappers with varying styles of exerting their voices, and a lot of the resultant songs have either high hats or similar sounding trumpets, or similar sounding drums, and in other cases, something about how the artists rap reminds me slightly of Three 6 Mafia's own style. I don't recognize any of the artists suggested, which is a good thing, it basically did what it was supposed to.
Next I picked a song by Bullet For My Valentine, not all the songs are quite nu-metal but that's because the song I chose isn't typical nu-metal (or whatever genre they were...) unlike some other metal bands they dont spend the whole song screaming, they actually do normal singing, so it picked up what to me sound like old school metal bands like Dio, Iron Maiden and so on... So it picks up on how some parts of the song are, which can get you mixed results, so if you want to find a similar artist down to the musical style, pick the most "metal" song you can find by them. This isn't an issue for me since I like some of those artists too, but I would rather get more bands that are more like Bullet For My Valentine, though it seemingly did catch one or two I had not heard of before.
Also tried another metal band Killswitch Engage with the song "My Curse" and it recommended another Killswitch Engage song titled "For You" which honestly, is weirdly close in style and I never noticed that before. Again this one's another metal band, I just wanted to see how it would do.
Lastly, I tried a Spanish reggaeton song, and I was not disappointed. You really did a hell of a job on this.
My only wish is that Apple would hire you / buy out your efforts because I wish this was part of Apple Music, their "suggested music" is awful, and the genre discovery type of thing doesn't always yield artists I remotely care for, I feel more inclined to listen to some of the suggested songs but it sucks you can only give samples and link to the song directly, if you could generate playlists from the results it would be good, this isn't a you issue, its moreso an Apple limitation.