Except when the bioessentialism has to do with their actual biology though, right? Wings, scales, breathing fire?
And mythic. If you're created by the God of Elves, and he thinks that his folk should be able to talk together, he'll imprint elvish in their mind when he feels like it, irrespective of where they are raised. You're an orphan? You were raised among humans? You don't have pointed ears because only one of your grandparent was an elf? Yet suddenly, at age one, you suddenly speak fluent elvish and asked for a longbow next Christmas, because bows are cool, even if you have never seen one and neither your parents, with their culture not being bow-using. They refused, but you told them they'll soon cave in, because humans are weak-willed.
Basically, culture can only accurately reflect cultural traits, which is why it's called culture. And while there are a lot of traits that are cultural, when you consider that elves are "haughty humans with blond hair, a fixation on bows, trees, have pointy ears and darkvision" and halfilings are "small, lucky humans with darkvision" and orcs are "big bulky humans with darkvision", well, when basically everyone is human, sure, there is no reason to have anything different than culture to express difference. But if one takes the time to make their groups fantastically different, culture can't explain everything.
It can't make you sprout wing, it can't make you know things without a tutor, it can't make you able to cast faery fire, and it can't explain why you never let pass an opportunity for squashing spiders.