English classes from elementary school to university aren’t accidentally in line with each other by some weird coincidence.

So who has the authority when experts disagree? Like I said, no one is saying "I house go" but some people think "Give this to whomever comes here first" is correct while others argue for "whoever". Descriptivism by definition seeks to explain how language functions. Prescriptivism only works within a narrowly defined framework, like APA or MLA for example, but even within those there's disagreement.