Yes, you can have realistic and cool/sexy/whatever. That requires a compromise because now you have two design goals instead of just one.
That's my whole point. It's just a perfectly legitimate stylistic choice. There's nothing inherently superior about "realism" as a design goal in speculative fiction.
Imo it's also a matter of consistency though. Both in terms of the art style over the series and in terms of the characters in the universe. In art style terms, I agree there's nothing wrong with throwing realism out of the window, but not after the series has already begun with an entirely different approach. I think the realism some people are speaking about is realism within the established MEverse. In ME1 they set the rules for what 'realistic' is, so going against those rules in 2 and 3 is a little jarring.
But it's not like they completely threw them out the window - most characters wear what looks like a functioning suit of armour, which makes the characters that don't wear it stand out sometimes, although that does depend on the situation. For the most part it was okay imo, but there are examples here and there which irk me ever so slightly. Samara's exposed chest, Zaeed's exposed forearm, EDI's everything. It's both the unrealism and oversexualisation. And don't get me wrong, I like sexy. I will admit to oggling Miranda and Tali's figure hugging outfits for an unhealthy amount of time. But while Miranda's costume suits her in general it's not exactly what I'd take to an uncharted battlefield full of alien monsters, at least not in the setting ME laid down, where technology makes sense and people wear armour for practical reasons.
All I'd say, for myself, is that there was a definite trend of style over substance. It wasn't everywhere, but it just wasn't necessary and was a little bit of a shame when ME1 had made me appreciate it's grounded approach to in-universe realism. If people preferred the later games' approach, fair enough I guess, but it's a definite change. ME1 got me immersed in a certain style, so for me anything that goes against that breaks my immersion.