I see that indirectly, Spotify likes to recommend me stuff that has gotten attention from a few specific human curators: NPR desk concerts, the Mark Radcliffe Folk sessions (a BBC program I believe), and A Prairie Home Companion. So it's not an either-or, I would not even have heard of those curators without Spotify.

But some of the best stuff Spotify has found for me, has had ridiculously few plays and no obvious human curator connection.

Bandcamp just isn't in the same league, and I'd say Spotify is far better on serendipity too. It's far from predictable what it will recommend, there's not many human curators you can say that about (including the three I mentioned).