Agree that Nylander is a better skater which allows his game to work in NA. Disagree he is in any way "gritty".
One thing to caution is nylander just didnt come over and make his game work in north america, I remember he struggled at first in the ahl and people did have concern about his game translating to since he liked to hold the puck for so long on his stick he sometimes got himself into trouble.
He was however stronger then pettersson at the same age and that to me is a big difference between to the two. I do recall concerns about nylanders game translating as well during the draft, heading into the draft he was my pick for us, he was amazing at the U18's against weaker teams and preliminary games, however when i tuned into the eichel usa game vs nylander it was no different then the pettersson criticism in that game, when the usa took away his time and space, he tried to make plays but ended up turning over the puck quite a bit, he had constant zone entries where the usa took away passing lanes and any room for him to work they essentially shut him down, it concerned me how his game would translate with less time and space and edged ehlers passed him for our draft spot, something i also regret and part of my learning process not to get to high or low on a prospect over a few games. Nylander of course learned in the ahl to make quicker plays and when he could hold onto the puck longer.
These things will take time if pettersson pans out, nylander being stronger then pettersson at this age made him more pro ready even though many had concerns about nylanders size as well during the draft just like pettersson he was still stronger, and that is the first thing that will need to be fixed over the season for pettersson before he plays a North American game where people like to tie him up against the boards. With that said I am not sure I see nylander pettersson comparison as much as others who like to compare them, they have very different styles of play. Nylander likes to hold and control the puck where pettersson likes to distribute it quickly and make quick plays.