I am not a Wentz hater and he got a big payday so good for him.
This was a fivethirtyeight article from a few years ago when he was still in Philly. Lots of statistical analysis referenced (Elo rating, etc.). I couldn't find the Elo rating from last year.
What I took out of it was that some of the blame went to the poor cast around him but he wasn't very good either.
Example - He was throwing into more tight coverages (maybe people not getting open) but he was below average vs other QBs when comparing to their throws into tight coverages also.
https://fivethirtyeight.com/features/carson-wentz-is-in-freefall-and-the-eagles-are-going-down-with-him/