It really is. I've never heard or read the word "Mexicanx" for example. It's just "Mexicano" unless you're exclusively talking about women and then it's "Mexicana".
Right but there's criticism to be had about language that erases a group of women once one man joins.
This is a problem not only in Spanish but in French too.
A group of Women: Elles
A group of men?: Ils
Add a woman to a group of men: Ils
Add a man to a group of women: Ils
In all cases the pronoun is determined by the presence or lack of presence of men.
Masculine as default is inherent exclusionary and patriarchal. This isn't American imperialism to point that out. It's just fact.