giving up a place in one of the worlds best universities because someone else said it is stressful is not a good decision in my opinion.

It isn't just "someone else" saying it's stressful. The work culture at Oxbridge is categorically more stressful than at other universities, particularly for maths. I know a large number of students who have dropped out of Oxford for exactly that reason, and I also work with many postgraduates who did their undergraduate degrees at non-Oxbridge universities and are just as qualified as their Oxbridge counterparts. The only people who put Oxbridge on a pedestal are those who don't have any experience of the system themselves. This is not me having a bone to pick with Oxbridge - as I said, I love it here and the system works for me. But given how many students here are on the brink of having a mental breakdown, if you genuinely have 20+ years of experience in mental health, you of all people should feel ashamed of what you're saying.