Skills level pretty similar, though Helenius has the edge in the skating category. Where Helenius clearly has the edge is how he handles the physicality of the game and how much harder he competes on 200 ft., just a never stop motor and great IQ Catton's 2-way game is somewhat overrated, you will see him glide on the backcheck and his game away from the puck needs work. Helenius is small, but strong, has no issue competing against growth men while Catton has his struggles against junior aged players.. The strength/power is what separates both players for me at that point. Its not impossible that Catton beef up and catch him up at some point, but unlikely IMO, Catton just seems to have a genetical small frame.
There is much less risks with Helenius than with Catton IMO, Helenius already projects as a solid top 6 center while Catton has the talent level to be one, but remains a long shot and is more likely to end up as a winger than a center.
I have Helenius a tier above, Catton in the 10-15 range.
I disagree on overall skill level; to my eyes Berkly Catton is clearly more talented as a puck-handler, corrals passes more easily with control, owns a better arsenal of shots, anticipates plays better, and his decisions with the puck are just higher-end. On a pure offensive standpoint, Catton's tools are just better.
That said, I do agree on most of the other points you've put forward.
Catton is a lesser defensive player than Helenius, is a bit more passive on the forecheck, not as adept at taking time and space away while defending the rush, weaker physically, softer, and, most important of all, Catton's skating just isn't as fluid or explosive as Helenius'.
Overall, I'd say that I think Helenius would be a "safer" prospect to project into the NHL compared Catton, with a clear path to becoming a top-6 forward and non-negligible chance at becoming a true-blue first-liner. If he fails to reach his potential, I still think Helenius could be useful as a complementary piece in a team's middle-6.
Inversely, I think that Berkly Catton's potential is higher than Helenius', with a clearer path to becoming a top player but also obviously more risk involved in picking him since Catton is more of a "top 6 or bust" type of prospect in my eyes, with more flaws to his game.
In a no-stakes game rating them purely on which player I like more, I'd probably have Berkly Catton ever-so-slightly ahead of Helenius because I'd prioritize his potentially higher ceiling.
But I think they each are tremendous prospects in their own rights, both definite top 10 picks in my eyes.
And I also think actual NHL teams, for which high (top 10) draft picks are by no means a small investment/loss if they make a mistake, might consider Helenius' relatively safer path to the NHL an advantage worth picking him over Catton's arguably higher ceiling.
So yeah, that's how I see things. Cheers and have a nice day.