Seems like a good deal. I'm not sure how much more upside Marchenko has, he's 24 so while that's not old, he's not really going to gain anything by default from just becoming a man. But it wouldn't be unusual (especially for an euro guy) to take a significant step in their mid-20s. Also last years team was not easy to put up numbers in, so his statline would probably get a decent boost just from the team becoming better even if Marchenko stayed exactly the same himself.
I mean Gaudreau was a 60 point guy with the 23-24 Jackets... and while some of that was just him not playing his best hockey and especially failing to convert chances, it was his worst season ever in terms of points/82 and he was still the best forward in the team by P/GP by some margin. It would've been interesting to see Laine play a meaningful amount of games to get some context, but I don't think he would've been P/GP in that team even if he was playing really well. I think it was just a really tough environment to score a lot of points in.