Another lecturer posting here. The rules operating at your son's institution seem bizarre to me (I work at a new university); there is no way anyone I work with would refuse to sit down and discuss an exam paper with a student, although we are told we can't give them back to the student to keep, so quite the reverse of yours. Also, he's unlucky in the 50/50 weighting of his course; that was the case for me as an undergraduate, but at my current institution it's 25/75 for 2nd /3rd year which supports the students who really buck up their ideas in the final year. However, you have to work with things are they are...
It does sound to me as though he has continued to think that his subject and being at university are just a continuation of A level work, when they are often very different. He has now got to play to his strengths. Ask him to sit down with you and go through the modules he has chosen for final year, and look at how that can be shifted towards essay-based and maths-light modules as far as possible, if that isn't already the case. Find out whether he can take any modules from other courses in his final year as options - my students are allowed to do this for one of their five modules, so if that applied for him he could try to sign up for a business module as one of his. His institution sound like they might be resistant to module changes, as they don't sound particularly struggling student-friendly in other ways, but get him to push it politely and as quickly as possible, so it can get agreed before the new academic year starts.
On the feedback question, I would want to push this issue of him not being allowed to discuss them with tutors. If he could go to the students' union and ask them if they are aware of this policy, and if not could they take it up with the university on his behalf, that might get him somewhere. It's accepted that you get less detailed/written feedback on exams than other forms of assessment but to refuse any at all is hardly good practice. He could mention to someone that he will be commenting negatively on that when he fills in the NSS (National Student Survey) in his final year.
I would also have a serious talk with him about asking for more help and guidance, and say that if he's not prepared to help himself it will affect the amount of support you are willing to give later on, as you're not going to be keen on bankrolling him after graduation if he could have done more to find out what is required of him while still studying.
Re changing courses, it might just be possible if they will agree for him to go into the second year of a business course. So you will have to pay for an extra year of him studying, but might get a better result. Don't count on this being possible, though, as some institutions (mine among them) no longer allow transfers mid-way as the first year modules are core to the degree you are ultimately awarded. It's definitely worth finding out though.
If that isn't an option, I would say he should finish and take advantage of the fact that to some employers, a 2.2 from a 'top' university will be perfectly acceptable. It annoys me that this is the case with regard to my own best students, who will be overlooked because of their institution though they are very talented and hard-working - but you may as well use that to your/his advantage. It would also help, though, to think about hobbies, interests or volunteering that would help him look like a more well-rounded person to prospective employers - i.e. someone who is a graduate but is more than just their degree. His university will almost certainly be able to inform him about volunteering opportunities and I would urge him to take up one of those. That might seem counter-intuitive given the academic pressures of final year, but it might also provide an outlet for him and be genuinely fulfilling. Sadly I don't think gaming as a major leisure time hobby is going to be that impressive on a CV so he does need to think about other activities.