That's really not surprising. To my understanding he was straight up miserable doing Age of Ultron with the Honest Trailer even saying "I think Joss Wheldon needs a hug."
That was after they said, "Guys, I think we...broke Joss Whedon." LOL, that sad little picture of him, so hilarious in its irony. But yeah, to think even a guy with a reputation like his, so beloved by the fan community still being bullied by the studio when he made the Avengers the success that it was. I mean, I have no doubt that Josh Trank's attempt at Fant4stic was just a complete misfire from the beginning and I don't believe for a minute that he 'had a really great movie we'll probably never see' but I would love to have seen what Joss could have done on AoU with no interference. I do want to hear him say the words in an interview, "Ultron would have grown more organically, before becoming twisted and sinister so it doesn't just come out of nowhere that he despises Tony Stark". Otherwise I think, as tragic as it sounds, that he may have lost some elementary screenwriting and character development skills over the years and that would not bode well if he did choose to stick around for anything in the future. But if he could say in an interview that he could have addressed a lot of the film's issues had the studio not given him so many restrictions, I'd feel that at least anything else he does in the future is still in good hands. I just hope the Russos keep up the good work with Civil War so we know them being handed the reins to the Avengers franchise is a good move. Since Civil War is basically an ensemble film anyway, this should give us a good indication that they'll be capable of handling Infinity War.
I hope we get some Iron Fist news soon. First they supposedly announced an actor, then it seems to have faded into the ether, now it's unclear whether they want to do it as a series or just a movie-length feature. I want some answers, even if they're not totally to my liking.