What has kept you from achieving C2, you’ve been there for 10y+
I've worked in German institutions for a long time now, I've published in German, I have no problems understanding people and, leaving my accent aside, people can understand me. I read books in German and understand German movies. My German is fine.
I could take time away from learning what's new in tech and science (a lot, apparently) to get a C2 but, and I may be wrong here, I don't think someone asking for "minimum C2" (which, again, disqualifies even native Germans) is engaging with the process in good faith.
I have no objections to learning the language, which is why I've done it. What I do object to is chasing a pointless certificate when I could be doing the thing I was brought here to do.
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.
When a company sets C2 as a requirement, it can be interpreted as "must have a degree from German University".
That's not true, but it is a commonly shared myth. I've taken and passed C2 with the highest mark in every category (I moved here when I was a young teen, wanted to know if I would pass it after hearing years of people saying things like you're saying).
Most Germans would easily pass C2, although I think they'd have to be well-read/possibly university educated to get high scores (mostly need to be able to read quickly, give a semi-structured presentation and write a persuasive essay).
For what it's worth, I could run linguistic laps around all the other test takers there that day, and I assume at least some of them passed.
For reference I scored ~C1 in German years ago (testdaf 4/4/5/4) and at that level there's no question at all about the vast gulf between me and an educated native speaker.
There's still a definite gap between me and native speakers, that shows itself primarily in the effort required, but I'm definitely near native (pass as German in all social settings, although an hour long conversation will usually tease it out due to my unfamiliar first name or small-talk topics, rarely but occasionally due to mistakes).
I prepared by doing two practice exams and about 5 filmed and timed practice presentations, and that was over preparing for me. Experiences vary, and I do think I'm a bit towards the outlier side, but it's left me convinced that the whole "native speakers might not pass C2" thing is overblown.