imo it just seems that way because of timing. In terms of comedic roles, Peter has more overlap with Morgan (comedic catalyst) and Jeremy with Danny (straight man role).
I mostly blame Jeremy’s decreased screentime on the fact that they never properly developed his friendship with Mindy…or at least not enough since S1 to keep par with Mindy’s friendships with Danny, Morgan and Peter. I mean, when was the last time Jeremy actually had a one-on-one scene with Mindy instead of being shunted to the B/C-plot storyline? I feel that the writers have really done Ed Weeks a disservice.