Someone forgot how Kakko turned senior defensemen inside out in world champs 2019. He has been asked to round out his game in the NHL and lost confidence in his offensive game. It happens.
He made quite a few really good NHL defensemen look like rookies.
To be fair, most of NHLers today are hyper skilled, so Kakko in NHL is just above a NHL average. He has good hands, not supreme hands, good shot, not a supreme shot, ok skating - not great skating, ok senses - not hyper-senses. Good at many things, not great ar one particular skill, but I would put play with the stick around the net is great. You get what I think of him? Outside NHL he is a star, at NHL level - he melts in.
I think he could melt in as a 2nd liner once he get more self-decisive about it. He convincing himself that he has to prove himself every training and every game, thats how you get very hard to play against. Practice his shot like Draisaitl, Marchand Pasternak - abillity to fire it away on an instant one timer touch, and dragshots with precision - and he could be a 40 goal scorer.
Confidence goes up and down sometimes, but with training, dedication and being decisive and determinted to do what you can to create, break plays, cover the puck offensivly, offensove bodychecks, be a passable option, practicing the shot a lot - and Kakko could be the best version of himself I think.
Overall I think a trade is good for him. Maybe a line with Berniers is great for him.