I get the source of this complaint, even if I think the context in which it exists should not be so easily disregarded.
Is Isabela “designed for the male gaze”? That’s a tough line to walk, certainly. Isabela is, without question, designed to be sexually appealing. I don’t think that’s the reason she was used in marketing, however— work on the trailer had to begin very early, and Merrill’s concept wasn’t even close to being finished. Not that Merrill would necessarily have worked even so, but it wasn’t even an option. Isabela was the only female romance available, so that’s what was used— whether someone believes that or not is up to them.
Is Isabela’s outfit/design “too sexy”? In the context of the fantasy genre in general, I’d suggest that her outfit borders on the demure. Not that the fantasy genre’s treatment of female characters is a great bar to use, but if you’re going to single out a character like this you should be aware that it doesn’t exist in a vacuum.
She also doesn’t exist in a vacuum within Dragon Age, never mind the fantasy genre as a whole. If Isabela was representative of all female characters in Dragon Age, I might have more issue with her appearance… but considering she exists alongside Aveline and Merrill, not to mention Meredith— a villainess who is neither young nor sexualized— there must be a reason for her being designed the way she is.
I’d say that reason is because it’s consistent with her character. When I saw the first concept for her my thought was not “oh God, why is she wearing that?” My thought was to nod and think “she looks great, totally appropriate for her.” If the concept for Aveline had come back with her having a low-cut breastplate with cleavage showing, I would have lost my mind.
Is she wearing appropriate armor? No less appropriate than Varric, the other rogue in the party complement. I wouldn’t say any of the armor in Dragon Age particularly strives for realism— nor does the combat system, with people getting regularly bombarded by fireballs and arrows, aim for anything more than abstraction— so it seems a bit odd, to me, that this is where it breaks down for someone, and thus a bit of a specious argument to compare Isabela’s outfit to a chainmail bikini.
There is a larger context of female characters being designed for the male gaze, obviously, which is the entire reason this argument comes up— but unless one is prepared to argue that every female character in a game should be designed solely in a non-sexual fashion as a reaction to that, the context within the game itself and what it’s trying to do really shouldn’t be ignored.
Personally? I adore Isabela, as I’ve said elsewhere. She could so easily have been a one-note character that never went beyond flirty one-liners, a roll in bed for her romance, and a sexy model at which everyone could stare. Sheryl did so much more with Isabela, saying something about empowerment and self-esteem, and if people want to only look at Isabela’s surface and judge her based on that— well, that’s entirely the point. She addresses this very fact in-game and thus I’ll always rest comfortably with where she ended up.