And, really... non-flamboyant armour would be pretty dull
I wouldn't call The Witcher's armours "flamboyant" - they were pretty realistic - but Geralt still looked stylish in them.
You're right, having only "exaggerated" armour is not the same as having only "form-fitting/exposing" armour. It's not that different, though: All female characters are beautiful temptresses who sacrifice protection for sexy looks, all male characters are muscular, brainless braggers who sacrifice mobility for showing off. If you look at it that way, it's both sexist.
Of course, you can also find in-character arguments if you want. Impressive armour might intimidate opponents, making combat easier that way. Revealing armour might distract opponents, making combat easier that way. Some characters could ask an armoursmith for exaggerated or revealing armour just for that reason. It's not very credible if every single (armoured) character in the game world apparently did that, however.
