I am a former Russell Group admissions tutor. I think your DS must make his own decision.
Light touch discussion is fine. Here are some things you and he may not have thought of.
Given that the course at the post 1992 uni ranks highly for both student satisfaction and employability, what components are pulling the ranking down to the bottom half? Is research the main one? Unless your DS is doing a traditional academic subject and a PhD is a possibility, a low research ranking should not affect his student experience. As PPs have implied, this may leave the staff more time to focus on teaching and they may be more interested in doing so.
Of interest to you both, even though employers are moving towards blind applications, evidence is emerging that a good education pays off. Specifically, in some branches of the Civil Service that have been doing blind applications for a little while, the percentage of Oxbridge entrants has risen. It is thought that this is because their training prepares them so well for the testing and interviews. (After reading about this on MN I verified it in the respectable press, but I don’t have time to chase down a reference now). How far this extends to other unis I don’t know.
Post 1992 unis broadly speaking offer more academic support to students than the RG, but this may have unintended consequences for your DS. How will he be assessed? In a number of degree programmes I know of assessments are more frequent than in the RG (again, broadly speaking).
Research on teaching and learning supports this. The best and brightest at Oxbridge essentially get it, in the form of very frequent feedback on informal assignments that are all but mandatory. Many, many RG students get away with learning less than they might because without any external need to keep up with their work, they don’t.
’Recommended reading’ in the RG may well become the subject of an assignment in a post 1992 uni. This becomes a theme.
If your DS is under the impression that he will be working less at the post 1992 uni, he needs to investigate the teaching, learning and assessment methods for his degree programme. It may not follow the dichotomy I have suggested. But many degree programmes do. The good news is that if he chooses the post 1992 and does the required work, he is likely to be very successful.