For some reason Bioware, in the last few games before DAI, decided to go for 'iconic looks'. Cynical me wants to say it was easier to design just one outfit for all the different companions/body shapes.
This desire for iconic (and never changing) looks drove the art department to find a signature look for each companion. Somewhere in the game files for ME2 I found a file that listed the companions as 'concepts' Zaeed was "The Veteran". Miranda was "The Vixen". This concept is what drove the style of all the companions. This carried over into every game since.
Since the goal was to put into visuals the character concept, no thought was given to "how will this look in combat". Therefore calling out Bioware on expecting Miranda to go into combat in high heels is missing the mark. Combat outfits weren't even considered. It wasn't even on their radar.
Now, I'm old. far too old (and cynical) to get excited over some sexy outfits on female characters. I find it crass and manipulative. This is what Bioware was hoping for though, players (specifically young male players, who I suppose they considered their primary audience) finding these characters attractive and wanting to buy the game because of this.
Take DA2 demo for instance. The demo ended with Isabela inviting the player back to her home for "company later". The message was clear. "Buy our game and you can have sex with this big chested pirate babe!". The scene was even edited from the actual cutscene to sound even more suggestive. Crass and manipulative.
As much as I tired of the 'in your face SJW nonsense' in DAI, I hope that game signals the end of this type of marketing for Bioware. It's childish and immature.
Oh, I haven't read through every page in this thread, but there was some discussion a ways back about the idea that 'sex sells'. Well, no it doesn't guarantee a sale, but it does guarantee that the target audience is more likely to pay attention to the ad. That's one of marketing's main goals. That's why ads on popular websites make that website loads of money. Eye catching ads get more views, and more suckers, err I mean potential customers.