So, what has happened to Josh's game? What is he doing differently? What is he doing wrong? Or what is he failing to do right? Are you saying he was never any good?
I've hypothesized multiple things on here before, some with evidence.
We know that his game style/play has changed and that has aligned with worse results coming from him. Why has his play style change is a tougher question to answer because I think there are multiple reasons, not just one.
1) His injury may have an impact things in the long run. He's played a bit more tentatively.
2) He previously deferred to his linemates to do things like break the cycle and transition the puck in the defensive zone, now he's being leaned to do so.
3) Maurice used to allow his defensmen have more freedom with skating out the puck, now he doesn't.
4) etc.
All of these, among others, can cause a player to still be equally talented but play worse depending on what play style works best for them (or for players in general).
I do also think that people overexagerate how good players tend to have performed, especially when they are young, home grown players. There is evidence in some models that Morrissey was never better than a #3 guy with some flaws.
Flaws can also be hidden hidden by a team. The Jets a ton of talent in overall really good players with Trouba, Byfuglien, early Enstrom and flawed but had their uses players like Chiarot, Kulikov, late Enstrom and to a lesser extent Myers.
It's also completely possible that Morrissey has peaked. Average peak performance age is 23-25. Some peak later, but some peak earlier.
It's also possible that ALL of these variables are true in some sense and all have mixed together.