If you watch any of the youtube video’s of live (or lip synching) performances you’ll note Joey (unlike the others) is clowning for the camera and repeatedly trying to connect with the bass player, who steadfastly ignores him. This might suggest some personality differences/interpersonal tensions in the band.
Of course this doesn’t change the fact that what he plays is perfect for those tunes. Whether he wrote those fills and leads, or whether Pete Hamm wrote them, I don’t know.
There have been threads about "the perfect pop song" here in the past and it seems to me "Baby Blue" and "Day After Day" are extremely strong contenders.
It's sickening that such creative people were treated so poorly.