I think there are multiple parts to his struggle in Nashville. I think he gets a total pass for the end of the 2018-19 season. His wife was literally in labor when he was traded from Minnesota and suddenly he's on a new team in a new city? That is a difficult transition with a newborn.
I think there was some early hope with a Forsberg-Duchene-Granlund line out of the gates in 2019-20, but it wasn't sustained. The Preds were constantly blending their top-2 lines trying to get everybody going at once. And it never happened. Granlund was always in the mix with the top players, though, he never got cycled back even when he struggled. Then when Hynes came in he basically decreed that Granlund was going to be his #1 forward, and suddenly Granlund was sometimes getting 20 minutes a night and killing penalties... he never got short-changed by Laviolette, but suddenly under Hynes he was elevated right to the top of the pecking order in all situations. He got something like 23 minutes one game. And he responded reasonably well, iirc he had something like 15 pts in a 20-game stretch or so, and we thought he might finally have turned the corner.
Then Covid shutdown happened. And a family tragedy with a stillbirth during that time. And he was basically totally invisible again in the play-ins when things started back up.
I don't think he had any chemistry whatsoever with Duchene. Duchene carries the puck a fair bit, and Granlund isn't really a guy to trail the play or support Duchene's rushes ideally. Granlund probably does better with the puck on his stick more often, and he didn't get that a lot. I always thought he might play better with Johansen who played more of a Koivu-style game, more physical and pass-first. But Johansen always had the historical connection with Arvidsson in that role instead. So in the play-ins, the Preds got great success going back to Forsberg-Johansen-Arvidsson, while Turris, Duchene, and Granlund all just looked totally out of synch and baffled with what eachother were doing on the 2nd line.
So I think there was a lot that happened in a short timeframe for him in Nashville, personally, and then on the ice compounded by our coach having outlived his time, our PP being a disaster the whole time, our lines struggling to find chemistry. Granlund didn't exactly step up and fix anything, but there was certainly plenty of chaos around him too.
All in all, I think it's pretty fair to just write off his Nashville time. He just needs to find a better fit and get settled somewhere. Let him settle in and find some chemistry and he'll probably do fine and produce ok.