Re: Restrainable
I think the difference is in how easy the Powers are to completely disable with a Grab, Entangle, or the like.
Birdman needs to maintain aerodynamic trim; any interference with his wings means he can't get airborne at all, even to hover.
Gleep's tail might be slender and flexible and easy to interfere with, although I kind of wonder if he's just trying for some free points.
Speed Demon can be hobbled or grappled, and he might stay upright or even struggle forward at a reduced rate. Hopping, if he has to, or dragging Gleep behind him.