The thing is, bringing logical elements of "real life" into your fantasy concepts strengthen them. You don't just drop reality at the door - this is still a world that looks broadly like Earth and follows the same physical rules.
Yes, you can just make stuff up, but that made-up stuff is more convincing if it's logical and all the pieces seem to fit together in a similar way to what we'd expect to see in a real-world analogue.
The Sahagin have many fish-like traits and reproduction is clearly one of them; thus it seems incongruous for the female to have breasts - much more than it seems for Garuda who is a one-off melding of "human woman shape" and "bird features".
This isn't just an issue I have with this because it's about "female representation" or anything like that; I was having much the same argument in another fandom recently over the fact that one gender of a mammalian race has tails and the other doesn't. That jars with me, and no amount of "it's fantasy/sci-fi so they can be anything!" makes it seem convincing.
Or back in FFXIV, it's always irked me that Xaela males have the dark eyes but females don't. It seems like something that should have been a clan difference, or possibly a gender difference (though I'm glad it isn't), but not somehow isolated to one gender of one clan. And yes, that detail bugs me more than the fact that a humanoid race has giant horns in the place of ears.
