> I dunno. The former places the cognitive load on the user. The latter places no additional cognitive load on either party.

It adds cognitive load because I've not seen a system where first/last name is not a synonym for given/family name, except it also indicates the system designer is not aware of alternative ordering for names and is forcing me to decide between correct order/incorrect semantic vs. incorrect order/correct semantic, so it's always a game of guessing what the system will subsequently try to display my name as if I enter it in a certain way.