The way I handle this is I separate Artists by || instead of ;
I have a virtual tag called FirstArtist defined as "$Replace($Replace($Replace($Replace($Split(<Sort Artist>," ||",1),-,1),',1)," ",),.,)"
I use Sort Artist rather than Artist here to strip of the "The" etc. The Replace functions are to strip out superfluous characters.
So if for example my Artist is "The Chainsmokers || Winona Oak" - the FirstArtist field will have "Chainsmokers"
I then define a CustomSort based on FirstArtist, followed by Title.