Are shards different?

[Cleretic]

Same with "mixed-race children are their mom's race", which was invented to explain why someone's half-elezen character looks like a 100% hyur.

Mostly unrelated, but this one actually does have something resembling evidence, because the two most known examples of mixed-race children in canon (Hilda and Arenvald) are both their mothers' race with some visual traits from their fathers'. Granted, sample size of two there, but works well enough as an answer for 'which race do I pick when making a mixed-race character'.

(Some people are definitely doing it because they're COWARDS who want to play a pointy-eared elf but don't want to go through the effort to make an elezen look good, but that's not really a lore question.)