We're used to looking at a pronoun's antecedent to determine its subject. In the sentence, "Jacob finally published a post he'd been mulling for a long time," we don't object that it's unclear whether "he" refers to Jacob. I don't understand why "The user receives the data they requested" is so fundamentally different. You still look to the antecedent; it's still clear.

I grew up taking great pride in "correct" English usage, but I now think insisting on gendered pronouns causes harm without any tangible benefit.