I was talking specifically about provision from lecturers rather than student ability, but we do have some excellent students that I would absolutely stack up against Oxbridge graduates. One of my dissertation students just won a very competitive national prize for her work from the subject professional body; many others go on to masters courses at RG unis and yes Oxbridge, and so very well. Yes probably the average ability level is below that of the high tariff institutions but we work extensively with them to bring up their skills levels. Yes, we (try) and teach them to write and put together a logical argument supported by evidence etc. Lecturers joining us from high tariff institutions are often shocked by the level of support they get, and probably a student starting elsewhere wouldn't need that - but it works (not always, certainly, but often). I have a student just graduated with a 2:2 and I was massively proud of them given the level at which they came in. Ability was hidden behind such largely solve-able issues as poor grammar, poor general knowledge etc. but came out in the end (they also got a perfectly good job locally, not high-flying by MN standards but a significant achievement for their family. Not related to discipline but you can't have it all!). Note they got a 2:2, not a first - contrary to what the media would have you believe, we don't just hand out firsts. Less than 10% of our students get firsts.
The issue of whether everyone should do degrees is a different one and yes I do see a lot of students who probably shouldn't be there (yet!). I'm as honest with them as I can be, but there's really not a lot I can do! Better counselling/career advice at school would help - NOT blaming teachers, who have enough on their plate, they just simply often don't know enough about their options to make an informed choice.
Al of this is just my experience, I don't doubt there are poor post-92 universities and departments - I'm also aware there are poor RG options too. Another ex-student of mine has gone to do a master at an RG MN darling institution and is very disillusioned. Apparently he already covered everyone in one of our second year units here!
Tldr: it's a LOT more complicated than RG good, post-92 bad. I wish our institution had the RG marketing team!
Over and out, I have to go teach!