Laine's home rink is a hybrid, not international. He'll require half the adaptation in comparison to players who come from environments with international size rinks.
BTW, Laine is far more useful without the puck than Puljujärvi, so I'm sure he'll be better in 5v5 than him. Have you watched them play? Laine was dominating vs Kärpät almost every shift, Puljujärvi was mostly invisible despite scoring some points. Do you know what the Kärpät fans were saying during the series?
Regarding injuries, well Laine was more productive earlier on in the season as well. In fact, in his first 33 games he scored 27 points.