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.
