One more response, because you're clearly making no attempt to argue in good faith.
The problem with Sylvanas's ab cutout, from a practical perspective, is that it doesn't protect her midsection from enemy attacks. Its benefits are a very slight reduction in weight and possible fashion benefits. This is not particularly practical. However, Sylvanas is a ranger. Rangers don't really wear armor to begin with–ever since Warcraft 2, their outfits have generally been a cloak and hood. Their "defense," such as it is, is the fact that they're supposed to be able to pick their targets apart from distances where their targets can't effectively fight back.
The Battlegear of Wrath, on the other hand, is very clearly designed for melee combat. It's big, it's heavy, and it's only equippable by a class who is built entirely around getting in melee and trashing stuff. So naturally, you have giant shoulderpads that block all peripheral vision. Those pads also have BIG FUCKING SPIKES on them that might look intimidating if you're a barbarian king sitting on your throne, but they're just as likely to catch on something, especially if you're fighting shoulder-to-shoulder with a bunch of other poor fucks wearing the same thing. Restricting upper-body mobility right as you get into melee is far, far worse than missing a section of armor over a weak spot.
Oh, but speaking of missing sections of armor, the Wrath gear also has absolutely nothing covering the upper arm area (because it's not like your arms are going to be exposed to danger during a swordfight or anything), as well as the most retarded helmet design in the history of armor. Not only is there a clear panel that extends in front of the ear to FURTHER restrict peripheral vision, but there is also absolutely fucking nothing covering the top and front of the skull. Stomach wounds, while painful and potentially fatal, are still less severe and incapacitate much less effectively than equivalent head wounds.
So, in short, Sylvanas's armor is vaguely sexualized, fairly easy to move around in, gives minimal protection overall, and isn't meant to be worn in melee. Battlegear of Wrath, on the other hand, is heavier, cumbersome, clunky, has a blatant weak spot so big and so obvious that it might as well have road flares bracketing it, and is (or was, at the time of its initial rollout) supposed to be the pinnacle of protection in melee.
I know which one I'd choose.