The Jets have had a pretty stable Top 6 of defensemen over the last 2 seasons. In descending order of 5v5 ice-time:
Morrissey
Pionk
DeMelo
Dillon
Schmidt
Samberg
Out of this group at 5v5, Pionk is last in: CF/60, CA/60, CF%*, FA/60, FF%*, SF/60, SA/60, SF%*, GA/60, GF%* , xGA/60, xGF%*, SCF/60, SCA/60, SCF%*, HDCF/60, HDCA/60, HDCF%*.
His PDO is 1.007 so you can't really say he's been particularly lucky or unlucky with on-ice SH% and SV%.
* He's the only one of these defenders who's below 50% in those categories, and the gaps between him and the next-worst defender aren't very close.
He's 2nd in PP time over the last 2 seasons. He has a GF/60 of 5.09, an xGF/60 of 5.79 and a SCF/60 of 42.46 - he's about as effective as Nate Schmidt (which is to say "not very").
He's 4th in PK time. He's about average in terms of Jets defensemen penalty killing (also not great).
He's spent the most time paired with Dillon (almost 60% at 5v5). His results have been equally poor with or without Dillon. Dillon without Pionk has really good 5v5 numbers.
Pionk is not an effective NHL defenseman and he's legitimately hurting the team. But the Jets are going to keep him despite him being an anchor because...they're paying him a lot and I guess he's a good guy in the room? Pavelec 2.0.