Well she is a ranger type, so she shouldn't really have 'proper armor' to begin with, drawing a bow with those shoulder pads and gauntlets would be impossible. But trying to bring logic and reasonability into discussions about blizzards armor designs is kind of pointless, male or female.
Sylvanas(at least since she became undead anyway) was always the 'edgy badass' of the windrunner sisters. Vereesa is much more modestly dressed:
And Alleria is gone missing, but would probably be something in the middle(the dota version is not far off what I would imagine).
Sylvanas is a bit of an outlier for Blizzard's female characters, along with a couple others I mentioned earlier like Alextrasza(who is a dragon aspect, so why would she need armor or clothes?). Most of the major female warcraft NPCs like Jaina, Katrana Prestor, Tyrande, Maiev, etc. are not dressed like that.
There is a pretty decent spectrum of female characters in warcraft, if you look past the noticable outliers.
