The thing is a degree shouldn't be "a degree", as you say.
Those grad jobs don't need a degree to be done - specifically they accept any degree subject and just put arbitrary requirements on the classification or awarding university due to demand. You could get a 6th form student who is bright but not necessarily academically minded, put them in an investment bank as a trainee (below the standard of grad analysts) and within two years they'd be easily able to do the role of a grad analyst. An analyst does not need or use advanced mathematics. A quant, sure, but most applying for those positions will have at least a masters if not a PhD, so..
What a degree should be is what it was originally intended for - an academic training programme for either a handful of professions which require specific academic knowledge to engage in (law, medicine, etc - also in modern day times, realistically engineering) or to continue in academia as a lecturer, scientist, researcher generally, etc, etc. Even some things, like a reasonable swathe of engineers, many solicitors (as opposed to barristers, and particularly in corporate law), architects, and so on, which would otherwise fall into the above, could well be trained (as they are, for the former two) in joint academic apprenticeship programmes - where the degree is incidental, more than anything.
Alas, (the necessary and good push for) access to university has been misinterpreted and misimplemented as meaning that everyone should go to university, rather than anyone should be able to go to university.