When musixmatch was just a lyrics software, it was ok. But now it is a full music player, and on top of that, its lyrics are often buggy and incorrect. External lyrics file support would let you correct and sync lyrics EASILY yourself.
Poweramp should have as much features as possible, but something not closely related to music reproduction like track identification would just make the app go up in size, clutter user experience and be hard on the developer. Also, keep in mind that there are awesome apps for track identification already. :-)