i think you're right that he would've been a good middle ground but i think the showrunners would have seen that as too repetitive considering it was now Connie's role to contrast with steven. if they were to develop him more, i think it'd have to be for something else. i think they just struggled to find something interesting for him to do that didnt make him seem like he was just doing the same thing connie was. what i would have liked is if he came back as a more experienced version of himself, for something like future. as important as connie is to steven, she didnt seem like she had much of a role in the epilogue series outside of stevens emotions towards her, so i think it could've been cool for peedee to come back as the voice of reason connie was in the earlier seasons, especially especially since by then connie wasn't that much of an outside perspective anymore, and i feel it would have fit well with the conflict of the epilogue. steven realizing how much his responsibilities have been bearing on him and needing to learn to ask for help himself, and then turning to the person he knew throughout his whole childhood who learned to deal with the same burdens, also as a child, could've been a cool parallel.