I think there's something we have overlooked about Kasperi. Bar his late teens, he is basically born and bred in the US. I think this affects him in how he carries himself, as a teen in a place he doesnt feel comfortable in (Finland) with the extra attention of the Kapanen name, expectation of a first round pick - Kasperi goes a bit into his shell, and doesn't come out as good as he is.
In the US, he feels more comfortable, English is probably what he thinks in, easier for him to identify - his name while being hockey aristocracy isn't that big a deal, there are many other first rounders, second rounders near him - he doesn't feel as cramped and is more confident, comfortable, and it shows on the scoresheet.
I expect for maybe 5 years Kasperi will be a good NHL player and disappoint in the Finnish national team, until he sort of grows up, gets more comfortable (out of teenage awkwardness) and then starts to play good for the national team as well.
No qualifications to say this though, part from having lived a significant portion of my teenage years abroad and had a difficult time getting adjusted back to life in Finland,