So, in terms of specific critiques of the offense (other than "shoot more threes" is the most vapid possible response to our shooting variability):
I read on FB that KP is drawing a foul on 34.0% of his post-up possessions, which is the best in the NBA. He also reportedly makes 69.0% of his FGs out of post-ups.
If those numbers are even close to true, why wouldn't we go to post-ups more? 41.5% of KP's shots are threes, which he hits at 35%. This seems like a misallocation. His eFG% on 2PTs is .649; it's only .525 on 3PTs.
He obviously has to shoot a certain number of threes to stretch the defense for himself and others, but it's odd that we don't post him more since it may be the most efficient shot our offense has.
You can see the stats here, so the stats you saw seem right.
https://www.nba.com/stats/players/playtype-post-up?dir=D&sort=FG_PCTHe is top 10 in both post up possessions (t-#8) and frequency (#9), but a guy like Jokic takes post up shots 9% more, Embiid 2% more, Sengun about the same. So there's room to do more, but he's not that out of whack. But Jokic and Embiid are both averaging 1.18 points per possession for post ups, while Porzingis is 1.40. So ya, you'd want to utilize that more.
But based solely on my eye test though, he doesn't seem like a dominate post up player. He seems weak with poor hands. Weak in that he can't really back people down or easily establish position, and his hands in the post are like how Jaylen dribbles (in that if he's doubled or swiped at or challenged, it seems like he often loses the ball). He's great at being tall and shooting over people though. (Does anyone else see that too, or is that an inaccurate observation by me?) So maybe he's so effective now because him and the team really choose their spots. I could see him starting to struggle/be much less effective if he went to the post a lot more.