Well, as most of you have done, we sort of have to say what the standard is before we answer. And since all of you are mostly right (they are all amazing players at their instruments), I sort of take it in a different direction.
I've played in enough bands to know that with appropriate time and repetition, almost anyone can get almost any piece under fingers. I'm always amazed (not in a good way) at guys in big name bands that can basically only play THEIR material. So for me, the real sign is, can they play outside their comfort zone, and outside their genre? Then of course, is, can they improvise and write in other genres, or in any genre?
I don't doubt that all five can do things in other genres, and maybe even fool us into thinking it's their main genre. But I think only one pretty much can play, write, and improvise in ANY context, and perhaps has no limitations on his instrument: Jordan Rudess. I can't help but think there's a genre out there that Mangini could play, but you'd be like "hey, listen to the prog guy playing that" and you could tell it wasn't his native language so to speak. Same with the remaining three. But I feel like Rudess really has no limitations on his ability.