Lots of useful perspectives here to consider. And options on switching course/college/uni if that is the right ultimate move.
But yes, shorter terms & being permanently surrounded by peers who were ALL in the top handful of students at the schools they have come from is tough competition!
And it is inherently designed to be competitive to continue to push every student there to be the best they can be.
That may be too much for him, or he may relish the challenge?
Once 1st year exams are over, make sure he talks to both course & college staff about his overall experience & options. Once he's had a couple of holiday weeks to decompress, he may have a better overall perspective from 30,000 ft.
In every high-flying cohort, there will be those running the country, companies, and making headlines in 10-20 years time. And those who will be doing extremely well for themselves by Joe Average's measure - but simply not quite in the same league!
There is no shame in being in the 2nd group, as long as he has some coping mechanisms in place to prevent comparison being the thief of all his joy! And the time & energy to add in some non-course activities which bring him a bit of diversity in his friendship group & some much needed fun & relaxation-even if it's from burning the candle both ends during super-intense 8 week terms.
I chose not to apply to Oxbridge because I wanted 'the most' student experience, not the shortest & most stressful... if he can reconcile his position with what he wanted out of it a year ago, great! If not, he's learnt some valuable things about himself & his learning patterns & interactions with his peer group which will be useful for the next 40 years. And it's not too late to tweak course/college/university to suit him better.
That is emphatically not failing, either way, & I wish him luck with picking his way forward from here, knowing himself a little better from the experience 