Garlean Inability to use magic.

[MikkoAkure]

There's some differences, though I wouldn't consider Maxima to be too far off of an Ancient in terms of his appearance:

I daresay it's likely a slightly tweaked model, even. Much in the same way as how Themius is quite obviously an altered Ramza and Varis' facial features are built off of those of a male Raen.

Maxima is just a male Elezen with a third eye and hyur ears. He has an existing Elezen face that may be tweaked just a little bit but what makes it more obvious is the Elezen-only hairstyle and the beard that already exists on one of the Elezen faces.

I’m also pretty sure all of the Ancients use Elezen bodies and faces as well, other than the proportions, there’s a lot of Elezen-specific hairstyles in Elpis.