"I think we sometimes forget just how high the bar for level C2 actually is! Even at the next level down, at level C1, I believe a person would already be good enough to hold down a pretty sophisticated job in a foreign country."
For me it's the opposite, I think we sometimes exaggerate how high the bar for C2 actually is.
Someone who has passed a C2 exam would be very proficient in a number of areas, but it's quite possible to pass the exam without being even close to that of a native.
When you say things like this: "But level C2 - or full native level", you make it sound like it's the same thing.
I have no doubt I could pass a French or Spanish C2 exam if I kept studying one of them actively for a few more years, and then one day I could get a job in France or Spain only to realise that the gap between C2 (exam passing ability) and "native level" is huge! The difference, however, becomes blurry if you get better at grammar, spelling and/or writing than many natives.
Returning to the topic at hand, I think:
- anyone can become a polyglot
- the first language is the hardest
- it takes DAILY study and exposure (2 or 3 times a week won't take you very far, even in an "easy" language)