He’s been disappointing as a third overall pick since the moment he was drafted.
His biggest issue has been his consistently issues; it’s been a problem of his since his season in the Liiga. He has struggled to prouduce game in and out, he has had hot stretches where he looks like a NHLer (like we’re seeing right now), but he has always then reverts back to going scoreless in 20 games. Reminds me of Galchenyuk in this regard.
The other issue with Kotkaniemi is his skating; he has an awkward stride that makes him look like Bambi out there on the ice; Because of his stride, he uses a lot more energy than his peers and is fatigued quicker than anyone else on the ice.
First point is wrong, he has been a disappointment to non MTL fans and people who don't consider some players (esp. European ones) need 4/5 years post draft to play a huge role in the NHL (see the Sedins, or were they a disappointment after D+4 ?). He was rushed in the NHL but he is learning.
Second point is very wrong, he is the opposite of Galchenyuk : KK is a lot more defensive, takes a lot less chances if he feels it may generate danger in his own zone. Galchenyuk scored 20 goals in his D+3 and 30 in D+4 in regular season, I don't think he was kept off the score sheet in nearly as many games as KK but he was responsible for many more goals on the other side (the play in Game 5 this year is the typical play showing why he was traded)
Your third point however is correct. I am not sure it is because the way he skates, or because he has had to take weigth quite quickly since arriving in the NHL, or because he needs to work on his stamina overall but he seems to be tired quicker than any other player. As far as this season goes, it may also be due to the fact that he started in the Finish Liiga before the NHL which added to the initial burden.