There have been players that don't fit all schemes. Chad 'Ochocinco' Johnson was a flop in NE. Looking at my Eagles outside of a great couple playoff games Blount wasn't that good. AP did fail in New Orleans. Bringing it back to Chicago, Greg Olsen just was a complete non fit for a Mike Matz scheme.
These things happen. Some good players just don't fit certain schemes. Nagy tried to fit Howard in last year and the results were what they were. There will be some sour grapes when the player does well after moving on, but it was not personal and some players just need a certain structure to succeed.
There is no real evidence Howard doesn't fit the scheme though. Yes Nagy prefers more versatile backs but that is a preference not a necessity. The point here is the Reid/Pederson/Scheme can work with a traditional back provided there is a back that is versatile on the roster. Hence why Pederson paired his more versatile backs with a guy like Blount. Hence why a team that passes as much as the Pats and who have James White and Rex Burkhead also have Sonny Michel. There is nothing special about Nagy's scheme that requires 100% of the snaps to go to versatile backs.
The reason Howard's results were poor last year is the same reason Monty's results have been underwhelming this year. The OL sucks. That is what all the data from three independent sites suggest. So unless there is some conspiracy between FO, PFF, and PFR not sure why people are fixated with blaming Howard for something that independent data is saying is the fault of the OL.
The easiest way to see this is in all the talk from people about how easy Howard used to fall down. They take one or two memorable examples of Howard falling down and create an entire narrative out of it. Meanwhile the data says Howard gained more yards after contact than the great Monty as people gush about Monty's ability to miss tackles. It is insane to me how perception can so easily overcome reality.