As a inverse example: a (German) family member has lived fully immersed for 20+ years in my Spanish speaking country.

I doubt he could pass a C2 level test, there's simply a hard limit in language learning for most people without academic instruction. It's also pointless, he's had a long career in a professional field where clear communication is mission critical. Furthermore even if another foreigner with a shiny Spanish C2 certificate appeared they would fare worse, because they wouldn't know the local social minutia.

Aside from jobs in the Literature department or something, a C2 requirement is a "foreigners need not apply" sign.