So far, I've only listened to the trio stuff. I have heard Parlan's trio with Stanley Turrentine on one of Mr. T's recordings so I'm really looking forward to hearing him with the Turrentines and Ervin. Isn't Grant Green in there somewhere as well?
For me, I wouldn't say that the trio stuff is weaker by comparison, just different. Given a choice, I would probably listen to a quartet or quintet over a trio more often than not because it is a little more interesting with the added layers, interplay and exchanges. The trio has a little more work cut out for them to keep your attention and Parlan's trio passes that test with flying colors. When I'm in the mood for a trio recording, these are surely going to be among the ones I reach for first.