https://musicbrainz.org/recording/161342cf-22b3-45f5-b13a-1c7b37d1c874
When tagging the above recording with "Use track relationships" enabled, the Performer "SixteenInMono" gets written into the "Performer" tag instead of the "Performer [instruments]" tag.

This might be intended, I have a suspicion that you'd have to specify an instrument for a more specific tag.
That's impossible in this case, as this artist has done all the instrumentation for this track.
Therefore it feels quite weird for artist having performed the instruments to get a "higher priority" tag than the vocalists, who properly get written into the "Performer [vocals]" tag.