Actually, you'd be incorrect. I'm quite tired of seeing "but the leather is PRACTICAL!" argument, because nothing could be further from the truth. Obviously, no one making that argument has ever worn leather pants in their life, let alone a full catsuit, or else they might realize just how stiff and movement-restricting tight leather really is.
Spandex, or if you prefer some form of exotic synthetic stretch armor weave since this is a comic book world, stretches and flexes with the wearer. It allows them freedom of movement without being restrictive. That's why ballet dancers and the like wear those stretchy tights and leotard getups, because nothing else would allow them the freedom of movement they need. Olympic gymnasts wear almost the same thing, for the same reason. None of them could do even a fraction of what it is they do if they were slathered in tight leather with clunky boots. It would be thoroughly impractical.