They should (and probably do, behind the scenes) have separate data fields for composer and performer. At least, I believe that labels will input those separately for each track, to enable correct tracking of compensation. Then Spotify will lump them together into “artist” n the UI, I assume. To make it easier for a casual user to find what they want. The “performer” Fanny Mendelssohn should probably not be confused with the Composer of the same name, and they should ensure this by using a unique id for each person rather than just a string field.