I'm not saying he doesn't have the potential, but I just don't think he will fulfill any of it with the Oilers franchise.
I reckon they'll get another top pick this year, and will focus on developing him. Pulju's going to be cast aside, because at the end of the day, he's a "high maintenance" prospect with his inability to speak English and accommodate to American style of play. It's going to be a whole lot easier to bring up a Canadian/American player who can already communicate, integrate into the lockerroom and naturally become a part of the team, playing a style of play that he's already familiar with.
On a franchise where developing a top prospect would be seen as crucial to the future of the franchise, maybe there'd be a chance for Pulju. But that chance is not with the Oilers. They've got McDavid, and that's really all they care about. They don't care to go to lengths, to accommodate Puljujärvi, when they've already got a designated top guy that they're building around.
If you put Puljujärvi with a franchise that lacks star players, a team that's really "all-in" on the rebuild, maybe they would be more willing to invest time and effort into him.