Either someone has a very very stupid idea of sixy and practical and battleworthy or they really think heavy armour is worn straight onto bare skin like a corset.
If they really think that you would wear the massive weight of heavy or metal armour onto bare skin like a corset, they need sacking from their job in design and are a complete and utter cretin
I'd bet that many designers aren't even thinking about "oh, there's X inches of padding beneath this" or "armor against bare skin". They're most likely going from a style standpoint, and not even considering stuff like that. (Outside, of course, people designing a 100% accurate history sim). With a "more realistic" style meaning
actually covered, versus the Heavy-Metal/Witchblade style pasties-and-thong, rather than historical realism.
Armour is'nt about being sixy, it is about not getting hurt and protecting you! It can look good while doing both.
Depending on the game, designer, and artist (heck, and the NPC wearing it)? It can easily be about being sixy.
And "look good" is subjective. We've got people here saying the Skyrim armors look terrible/unimmersive/etc because of the minor female shaping they have. You've got people saying that they're really plain. You've got people in the "best looking armor" threads saying that Armor A is great, while B is terrible; and other people saying the exact opposite.

Personally, I'm fine with the utterly impractical silly/sixy armors.... as long as they match the style of the game they're in. So the wildly couture armor in some of the Korean MMOs? Look fine in those games, but would be out of place in Skyrim. Meanwhile, the pretty-puritanical Skyrim armors also look fine - because they match the tone of the game around them.