After watching a few games of his I'd describe his skating as clunky, It's not even the speed I don't like but the stride and overall mechanics. Can it be remedied over time? Maybe, I'm just not sure how likely that is as I'm not good at projecting what these young guys will look like in 5 years, I simply don't have the experience. So I take it at face value.
Other than that I'd say he plays a smart, methodical game. But my worry is how he translates that to the NHL pace. Like you said he can slow the game down, it seems to be the primary way he plays, but I'm just not confident he'll be able to do it in the bigs. So if I'm going to take a small center I'd much rather have Rossi, who I think varies the pace of his game much better while also being considerably stronger on his feet despite being smaller.
What I do love about Perfetti is his wristshot, his release is niiiiiiiice. Much prefer it over any of the others outside of Holtz. But still, just too many "ifs" for me for 4th overall. I could be wrong of course, lots of people who know way more than me seem to really like him. But outside of his production and shot I don't see a lot to be excited about.