Hi, OP -
Sorry I am late to the party. This is an interesting one. You have a lot of good, practical advice here and the first thing I want to do is support the idea that your DS at least look into apprenticeship schemes. They can be utterly fabulous but as @TizerorFizz says, they are in very short supply and extremely competitive.
This thread reminds me of one from a little while back from someone who was a bit light on Maths for an Economics BSc from Warwick and perhaps their other top choices, but well suited to some of the strong BA programmes in Economics. People wrote in describing what they or their children had done with Econ BAs. They had perhaps needed to be more proactive, but they had been able to make good opportunities. That’s the sense I am getting about your DS, and I think @PerpetualOptimist seems to understand it well.
To the specifics: I think we have another tough year ahead. I think Warwick is likely to have a strongly mathematical approach, based on what you’ve said and their general reputation. But I don’t want you to take my word for it. Admissions tutors want to help, ideally at their own convenience. The best thing would be for your DS to contact Warwick and Bath by email laying out his PGs and qualifications, possibly including a suggestion I will make below. See what they say.
Unless they are both highly discouraging (my guess is that W will be, and B will temporise), I would apply to at least and probably only one of them. The suggestions of Lancaster, Leeds, Loughborough and Sheffield are all excellent and I am sure there are others of this calibre. Manchester? Glasgow? I would likely apply to three of them. I would also apply to one dead cert.
I fully agree that your DS won’t be needing trig, but he will be needing a fair amount of statistics. And the maths training helps with general analytical skills. I am wondering whether your DS might do an EPQ, over the summer and into the Autumn Term, bringing statistical analysis to bear on a geographical business problem? Perhaps some aspect of the worldwide shipping crisis, and/or the shipping container problem? I am sure there are many other topics; that is just the first one I thought of. He would be making the case for his ability to do the relevant maths whilst highlighting the relevance of his Geography A level to Business. This is what I think he needs to do.
I don’t know timings for the EPQ - whether pupils need to sign up at the end of Y12 or get some preliminary approval at the beginning of summer, etc. There is no explicit timetable, so it would be down to the school.
I think students on a Business pathway are much more employable if they pick up rudimentary tech skills along the way. What that will mean over the next four years and in the specialism of your DS is anybody’s guess. I also think these students need to be proactive and start making their own opportunities almost from the moment they arrive on campus. With those caveats in mind, it can be a fine field of study.