> There do exist prescriptivist linguists

That is not true, at least in mainstream serious academia. Prescriptive linguistics doesn’t exist any more than prescriptive biology or astronomy.

Maybe in the USA. But bodies like the French Academy and many similar ones in other countries very much do issue opinions on correct grammatical (and vocabulary) usage. And members of these institutions are very much considered the top of their field in their countries.

The members of the French Academy are not linguists. They are mostly writers or academics from other fields (history, philosophy, etc). If you can read French, check here: https://www.academie-francaise.fr/les-immortels/les-quarante...

> And members of these institutions are very much considered the top of their field in their countries.

Maybe, but their field isn't linguistics.