Something worth pointing out, last year Kakko finished with 37 EV points, good for the top 120 in the league for forwards. Purely from a numbers standpoint, there's 192 top 6 spots in the league. So make of that top 120 position what you will. He's in some good company with those numbers, there are some very good players in that range.
Anyway, Kakko spent ~530 minutes EV with the Chytil and Laf line. ~230 minutes EV with the Zibanejad and Kreider line. A handful of different variations but those were the main 2. He put up 21 points on that Chytil line and 8 on the Zibanejad line. So he did produce at a higher pace on that Chytil line, not just in terms of the overall numbers. Not by a huge margin but its worth making a note of. Chock that up to whatever you want, better chemistry with the kids, easier matchups... either way, the way that Panarin line is rolling with Vinny and Laf.. Chytil probably slots in between Kakko and Cuylle, that could jumpstart the kid.
Chytil was crucified 2 years ago centering that struggling line of Gauthier and Laf. Deadline deals reconnected the kid line toward the playoffs and they had a real strong showing that year. Kakko seems to be in the same boat, his "stuggles" this year seem to really be more indicative of how inept that top line has been