The thing with Woo, is that he was already a pretty rocked up prospect. He had a small frame that was already pretty filled out by draft day. There was very little room for physical growth and development there.
Whereas...
At the combine, Mynio rang in at 6' and 1/2". But 163lbs. Which is obviously insanely light for that size. That's the profile of a prospect who is still growing into their frame. It's where i think the whole impetus behind this pick lies. It's a guy who is a pretty serviceable defenceman at the CHL level despite that lack of bulk...but in theory, that provides him a lot of room to physically grow and develop. Along with that, you often see significant improvements in terms of not only the strength to handle things defensively, but in terms of explosiveness in the skating.
That's the big weakness right now. He's a bit..."bambi-legs" as a skater. If he can grow into his frame and add power and coordination to his stride, there are the foundations of a pretty decent skater there.
@MS mentioned Sautner. But i don't really see it that way. Sautner was a free pickup who developed into a viable Pro caliber player late in his junior career, but did it mostly through development of his game, not his frame. Mynio to me, is more like Jeremy Lauzon. A really spindly player who did alright but is clearly still growing into their frame and lacking power as a result. The skating is a similar sort of point of contention with both. There are some decent technical foundations, but seriously lacking dynamic power and often looking a little bit...crossed up when pressured.
That's the thing for me, where most of Mynios skating issues come when he's forced to move his legs faster than his brain seems calibrated for. Lauzon was similar. When Mynio can move purposefully and is dictating that movement himself, it's a lot less cumbersome.
Who knows what actually happens with him developmentally. But to me, he looks like a 160lb kid who is taller than he knows what to do with at this point. He's not a heavy footed or overly awkward skater in general. He just looks to me like he lacks real power and authority behind each stride, and doesn't entirely trust himself to make really aggressive change of direction type moves.