I teach at an RG and attended 'Oxbridge'.
A long time ago now, but I remember a sense of victimhood in the first couple of terms and that others must be having it better. Why were friends at just-as-good universities having an apparently great time and only 3 essays a term, when we had 2 essays a week?! In retrospect this was down to feeling that we didn't quite fit, and that people with the kinds of lives and careers we had in mind (unflashy, public sector) often did go elsewhere.
The social life seemed very limited at the time - very masculine college bars, very old-guy or touristy pubs, a handful of terrible nightclubs, formal dinners, sports team drinks - generally very alcohol-focused.
It improved gradually as colleges and departments introduced cafes and the hospitality sector improved, and it got easier for students looking outside their college for a social life to find it.
On contact time - our norm, typical for RGs, is about 3 contact hours per 20-credit module per week. We have two semesters: a 12-week teaching term inclusive of a reading week and revision week. So students are generally around for 12 weeks each semester, no different really to 3 x 8 week terms.
The way we teach is intentionally different because we have larger groups, use lectures/seminars rather than personal tutorials, and different expectations of how much prep students do. The best students do study full-time - some even try and keep a 9-5 routine.
Everything students need to know to get their good 2.1 is in the teaching materials. Students can still be creative and read off-list - it's great when they do, just quite rare. We often see them a little more often in personal meetings during the revision/assessment period after the teaching period.
There are attendance and engagement issues, which were building before Covid - and have affected students socially and emotionally too. On the teaching and learning side, students like the option to watch lecture videos after lectures, so that's provided. But this reduces in-person attendance, particularly when the lecture rooms are further off the beaten track, or dingy, or the lecture is 9am or 5pm. It can mean teaching gets very small-group though designed for larger groups. A lecture designed for a group of 20 could have 3 students if at 9am in a week when they have deadlines for other modules. Lectures have become more chatty and interactive, but there can still be a sense that the teaching model is not quite right given how students now are, just for different reasons than the Oxbridge case. Lecturers with more seniority, or teaching larger modules, don't have this issue so much. So students tend to have a mix of experiences, from big lectures to accidentally-tiny seminar groups.
Students tend to gear their effort around assessments - whether weekly essays as at Oxbridge with exams at the end of a three-year degree, or more periodic coursework/exams elsewhere. Modules now may have (for example) 1 formative piece of work, a shorter (e.g. 25%) summative and longer summative assessment each. So for a standard non-STEM programme with 6 20-credit modules a year, you can work out the general contact time and assessment load.
We have some very bright students, and ability ranges are quite narrow - for a course with an AAB tariff, most of the students will have AAB or above because that's the way university entry works. I'd say that RG students also have the feeling of being a small fish and anxiety about suddenly not leading the pack. It's tough for some students to have to stop relying on being smart and the quickest on the uptake, if that's been important to them - especially when university teaching values research skills and consistency rather than effortless ease, and increasingly so.
My one thought on looking at the OP's message is that York is hardly a very different city in terms of size, medieval buildings, city nightlife - though the difference in teaching delivery, university buildings etc may well appeal. One thing that is good for students at Oxbridge is that their tutors get to know them personally and often remember them for years. This may be changing slightly as tutors are increasingly on temporary contracts or unable to afford living in the city, so don't stay for decades as in the past.
With Oxford's 'optional' lectures, you can attend those outside your own modules, a brilliant thing to do. The copyright libraries are an amazing resource. The language classes open to all students were excellent. I went to graduate seminars outside my subject, and spent a lot of time reading novels in cafes. I eventually got a part-time job and started volunteering. It's not easy if you don't feel you fit in. But some of us will have that feeling wherever we go in life, and it really is what you make of it.
This student could do very well at York and it probably won't make a big difference in the end either way. It would help both him & the OP if they frame it as having genuinely learned a lot from a year of personal tutorials, having had to do Anglo-Saxon etc and done well at it (it's good for students to do something difficult), and the satisfaction of good grades in Mods, before moving on. I presume they would stay on alumni lists and might also have access to things like the Careers Service for a little while. He should keep in touch with friends he made, and can get a visiting card to the Bodleian - just see it as moving on, as everyone has to do eventually.
Lots of people do visiting years e.g. as international students with no qualification at the end - so should see it in those terms. Still being educated and extending horizons, then doing something else. (By the way, he wouldn't get student loan finance for a year abroad - students are allowed one 'extra' year.)
Make it a positive choice - so he uses his time at York to genuinely learn what he can & take full advantage of what they and the student community have to offer. He should make sure he builds his own academically-elite educational experience, and make full use of his brain and his time.