There are plenty of players not doing as well as Pettersson who were nevertheless brought over early in the season. Kevin Fiala and Mika Zibanejad immediately come to mind, in addition to Nylander. My only point was that players who are even holding their own in the SHL don't generally stay there for the full season, historically. Pettersson's statistical performance is a function of both the level to which he was able to dominate but also the situation that allowed him to play the full season.
In the past, a player with 21 points in 20 games or whatever he had probably would not usually have been left there to finish the season on a tear the way he did.
None of this changes the fact that his performance was extremely impressive to the point where it is very hard to even find any comparable players. I find it very frustrating that discussion gets stifled in here because if you say anything less than "Pettersson will be the greatest player to ever wear the jersey" then people get defensive and accuse you of trying to "diminish" his performance.