Well, this is a fantasy game ,but how "real" are we getting?
Champions like
simply don't exist.
Champions like

ninjas or assassins, contrary to what most people would think, assassins did not wear special black or sneaky outfits. They wanted to blend in so they wore regular clothing. In our day that would mean a t-shirt and pants. In leagues day whichever cities attire was common.
Champions like
Would all be severely damaged or close to, probably flat chested (except maybe Illaoi) as the fat in their bodies would likely by non existent. And would look like some of the strong women of today.
Champions like
Would probably just be midgets?
Certain champions that would wear more fitting attire instead of "sex sells" gear would be.
noble outfit formal something akin to
More elegant or showy outfit something like
except purple? lol
an actual uniform.

something warm like
etc.
Really good cos players? Or if the existed then likely exactly what they look like. Rengar might have something to shroud his white fur unless he has an actual cloaking device.
Trying to think of how this can realistically happen. I'd imagine the process to transform like this would be excruciatingly painful. I'd doubt any of these could realistically transform ever. Shyvana would be walking around with 300 tons of flesh behind her at all times.
Nid looks the part she looks like an Indian or Primitive, no real reason she wouldn't have her hourglass figure, i'm sure she'd be healthy.
Skin and figure Shyvana would look the way she does, but a lot more armor to hide the fact that she is a dragon and general protection, unless that interfered with her transformation?
Gnar as with most wild beast or monsters would probably just be naked. Letting it all hang loose. lol
Other then that you have odd balls like MF that could wear that for reasons, but can be argued otherwise. In fact all of these can lol.