NHL is easier for younger players than AHL? That sounds funny. Yes you play with better guys but you also play against much better players there is reason why younger players play AHL to prepare themselves to the NHL. I agree that NHL is more structured but it still whole different world than european large rink. At WJC’s Heiskanen looked shaky because he seemed to be hurry all the time because he wasn’t used to fast paced small rink game. Välimäki and Jokiharju in the other hand looked that they had all the time and space in the world.
Dallas stars is having huge pressure to make playoffs next year. They have really talented group of players but have failed reaching playoffs last couple years. They will pick best team from preseason. I think that Heiskanen will have shot to prove that he belongs to NHL but it is far for certain him to be in NHL roster or be effective NHL player for full season.
I disagree with your point that Heiskanen looked "shaky" at the world juniors. Heiskanen wasn't at his best but far from shaky even with his injury. His poise and defensive iq at the wjc was on full display, it was his offensive game that was hindered. He did not show off his offensive game as he was just attempting to keep it safe limiting the effects of his injury. If his game was shaky his coach wouldn't have had him one of the leaders of toi for the wjcs.
Players like Heiskanen, who have exceptional hockey iq, dont take long to adapt. He is going to be in the NHL next season unless something unexpected happens, unlikely but he might play in the AHL for a handfull of games but will quickly show he is too good for the league. Klingberg came over after never consistently playing on NA ice and he instantly dominated the AHL with ease. Pressure of the stars should not even be considered, hes a very confident kid so he'll handle it with ease. I believe and predict that he will make the NHL roster next year out of the gate but play him in a semi limited role and as his confidence and slightly needed adaptation occurs his role will gradually grow throughout the season.