I still think Kakko has some untapped potential in him. I'm not writing him off from becoming a very good 50-60 point 2-way winger who owns possession and the boards. Think a passing version of Kreider
IMO Kakko has Jake Voracek potential just in terms of playstyle. Physically strong, strong on the puck, but not impossible to knock off the puck.
To get there, though, he has to get faster/qucker acceleration, meaner, and shoot more.
He's not going to create the space for himself that he needs playing such a clean game he's <20 PIM every year. He doesn't have to fight, or play gritty, he's just got to be enough of a PITA to play against that Dmen on dead end teams give him space b/c they don't want the hassle and they're playing for a contract, and Dmen on decent teams think twice because if they get aggressive with him, he'll dish it back and it might hurt.
Part of his struggle IMO is he's trying to play a big style to create space for himself, while not doing the little things that will give him more space.