I checked in Wikidata and we have 135 124 items linked to MusicBrainz artist-ID see Property_talk:P434 and just 5320 items linked toSpotify Artist ID see Property_talk:P1902
Is there an easy way to get all artists with a Wikidata ID and Spotify Artist ID and for those also the MusicBrainz artist-ID
The Spotify information here is not added by bots, it should be pretty much all added by humans (and same for the Wikipedia/Wikidata links), so it should be reasonably safe to reuse.
Wikidata does require human confirmation for fully automatic matches, in general
Of course, there are some Spotify “artists” that aren’t properly disambiguated and might belong to several different MusicBrainz/Wikidata artists, but hey, at least with the constraints on Wikidata that’d be easy to find and try to fix.