It turns out my problem was not as bad as I thought initially. My problem tags were limited to only a few thousand tracks, and most of those were albums which were supposed to have two artists listed. I created a static playlist named "Known Multiple Artists." I added the albums that are supposed to have multiple artists, and then added "And Not in Playlist" to the Auto Playlist. This narrowed it down, and I was able to use Advanced Search and Replace to fix the Display artist for the remaining files. I added them to the static playlist, and now I have a way to easily check for this in the future.
If I search on just "Artist" instead of "Artist: Artists," I just get files that have ";" in the actual individual Artist fields (the listing shown in your third screenshot).
I recreated the problem to check this, because I swear I tried it, but it didn't work. My problem semicolons were only in the "DISPLAY ARTIST" field, and not in the "Artist" field. Using an Auto Playlist to find "Artist / Contains / ; " finds zero tracks.
I think I treat my Artist tags differently than others. I would rather have multiple tags, than one tag with multiple values. I feel this makes the data easier to search, and it makes my tags more portable. This way, I don't have to be concerned about which separator is used. Maybe I'm wrong, but this fits nicely with my library storage scheme.