"Why do quants with PhDs earn less than bankers with bachelors degrees?"

An MBA would seem to be a logical choice. It's just a 2-year commitment, and some companies (not sure about asset mgrs) will sponsor / defray some of the costs. There's much written and said about the relative virtues of top MBA programs vs. others, so your mileage may vary.

But the MBA is basically a survey of multiple disciplines, and of course that implies it's rare that you'll find all of them instrumental in whatever job you do afterwards (only some will be useful).

What the MBA will accomplish (and maybe it's an overkill way of getting it) is it can give you the skills to solidly assess your personal risk profile throughout your career, and give you a clearer head (and less FOMO) around the choices you make, and those you pass by. (That's a benefit that's more concrete later in your career, rather than earlier.)

Maybe putting it another way: the MBA should help you manage the process of multiple reinventions of yourself and your career that you'll likely need to accomplish during your working life. (You can get lucky, and have the stars align, and wind up at a wonderful company that will serve you well for decades, and not be cyclical enough to ever lay you off. In that case, the MBA would almost certainly be superfluous. But keep in mind that, if you pursue a highly-specialized path, like the one you're on, and don't stray from it, there will come a point where you will be expensive in terms of the incremental value-add you offer, in comparison to a somewhat more junior colleague, and you'll be the easiest head to chop when austere times come around, as they inevitably do. So, it helps to have acquired some skills of resilience along the way, and I think the MBA helps with that. Not the only path, but one with some reasonable benefits and not onerous compromises, imho.)

Degree, Qualification and Education really don’t matter in Banking. From my 20 plus years of experience, I have seen a Banking Apprentice become CEO, many MDs and Directors without any graduation degrees and A level pass qualification. Better qualification, education and knowledge don’t guarantee you that you will be successful in your Banking career. That explains why Banks often fail or create economic chaos or get involved in the scandal. The key reason is the quality of people at the Senior Management is not adequate, many wrong people get promoted to the senior management because of their long stay in the company, race and ethnicity without real intelligence or caliber. Most banks fail to change this horrible and annoying culture.

Because your calculations mean nothing if the deal doesn't go through. Your work is very important, but it has to be used appropriately to generate any value out of it.
Farmer earns less for their work than the superstore.
Dairy farm owner earns less than the ice cream company.

PhDs know far more than all others in terms of analyses, modeling, and forecasting. Those who disagree don't know what they don't know...but they think they do. That said, being a high end Quant does not mean you have the more innate abilities, such as what it takes to BS a client into moving forward on investments, good or bad. Having only the PhD level abilities or the BS abilities limit one's real success. The PhD may never close a deal, and the BS guy may bankrupt a client. Better to have both.

Having a PhD in physics doesn't mean you are entitled to earn more than someone with a BA, it just means you know more about physics. Besides that, there's a risk premium associated with a client facing buy side career. You may earn more in a good year but a few bad years and you'll be out. Quants probably have higher career earnings on average but with a lower variance.