Herrera, Kagawa, Hargreaves (for us), Mkhi, Blomqvist from earlier eras perhaps, Schweinsteiger (the version we got), Matic - From this current era, I'd put McTominay in there.
Park imo was a squad player but was excellent and still got a good amount of minutes, almost a like for like sub at times - He would've made it to the first team at a lot of other good clubs, he just came into United during an era where we had world class midfielders and wingers, I think a player with his kind of commitment would have easily made first team regularly at United in this current era.