I sort of agree with your statement, I wish this skin had a bit more effort put into it rather than the whole joke being executed, which to be frankly honest, is an old and not-so-original joke.

However, I don't see the cultural appropriation issue, the skin is very obviously based on Mexican designs, but a lot of Warframes are already based on other cultures. Atlas is based on another culture himself, it seems strange to complain about it here. Although, I will complain about how it was used, since it's pretty tasteless.

This is subtle as the Mexican Gandum that came from the sambrero space station and I wish I was making that up.
If this were really thought out the artist would find other things in mexican culture or mythology to draw inspiration from and not just a boring stereo type.