Just want to make clear me bringing up Sprong wasn't "that's who I've heard Koivunen is", it was more using the most familiar example to point out that being the leading AHL rookie scorer only guarantees so much. Technically ahead of Sprong (but in a lot more games) that year was Mason Appleton, who never cracked 40 points in the NHL. And those are some of the good outcomes. Top three from 18-19 - Barre-Boulet, Cooper Marody, and Tyler Benson - are all out of the league. Go to 21-22 and it looks like Jakob Pelletier is following them, Jonatan Berggren feels 50-50...
In fact, Sprong might be the most successful such player out of the period I looked at bar the huge successes of Josh Norris and JJ Peterka. Logan Stankoven probably goes on to be good, Formenton probably is if he's not a dirtbag.
I'd suggest that 90% of the time, a forward who spends his entire rookie year in the AHL simply doesn't have the skill and vision to dictate at the NHL level. They might have the skill and vision to play off of a guy successfully, but to play off of someone, they need to be pretty complete.
We'll see what happens next but I wouldn't be surprised if he doesn't kick on because he doesn't have the athleticism to get separation. Which, sure, as 5th best prospect in a non-prospect rich org isn't awful. Although if I'm comparing him to Murashov, I think maybe I prefer Murashov's chances.