This^
The cleavage window also takes away from the seriousness of the character.
I don't have anything against stylish armor. But you can have armor that's both stylish and reasonably practical. Cleavage windows are not practical.
Still catching up, but wanted to reply to these two points - the reason I don't mind it is that the males tend to be equally as tragically dressed. Wei Yan's entire abdomen is constantly on show, despite him being characterised as a berserker melee fighter who gets in close and personal. Same with Deng Ai - his sternum is exposed to show his manly chest, and his armour reveals most of his arms and legs.
To contrast, Wang Yi has always come across as more of a tactician you can play as, à la Zhuge Liang or Sima Yi, rather than a protective tank, like Zhou Tai or Huang Gai (whose armour is also very impractical, usually being portrayed as showing off all of his chest). It doesn't seem particularly egregious to me, within the context of the game.