How many legions are left and what is the status of them?

[Kesey]

The IVth is the most interesting and fleshed out legion so far but It feels cheapened by the fact it's breaking the rules established in the lore that non garleans can't be legates. I'm hoping for some kind of explanation that makes sense cause it seems like a lazy retcon, especially when it's implied to be the case even before garlemald was officially classed as an empire.

I think the limiting rule is Garlean citizenship, not race. As all Garlean conscripts are offered citizenship after 10 years of loyal service. So by serving faithfully can grant citizenship and then by extension allow for promotion to legates.