Linguists don’t say varieties are right or wrong (even though they might have private aesthetic opinions like everyone else). That would be like a biologist saying dogs are the correct version of mammals and cats are wrong and/or don’t exist.
https://www.scientificamerican.com/article/cats-are-perfect-...
That is not true, at least in mainstream serious academia. Prescriptive linguistics doesn’t exist any more than prescriptive biology or astronomy.
> And members of these institutions are very much considered the top of their field in their countries.
Maybe, but their field isn't linguistics.