Commercial work will always pay better than academia. Roles like trader/quant where your value is measurable & portable will always pay better than being a drone in a big machine like Google. If anything, front office finance roles aren't underpaid: people with similar skill sets are underpaid elsewhere.
I don't work in trading anymore, so I'm not talking my book here. Trading is zero-sum at a transactional level, but has knock on benefits beyond profit and loss:
-Making it easy for companies to raise capital through IPOs or offerings (without a robust secondary market for securities, people will be less likely to invest)
-In commodities: Letting businesses bear the risks they want and insure against the ones that aren't their core business
-Liquid markets let real people trade in and out of investments without friction at fair prices
-Providing accurate price signals to other businesses and the broader economy
So I don't think I was saving the whales, but I don't think it was wasteful, either.
Also, as a mildly clever OCD math guy who's semi-good at writing fast C++ code, I don't think I would have been curing cancer anyway.
ETA: At least in the case of HFT, if you accept that markets need intermediaries of some sort, it seems more efficient to have a few dozen tech/math guys do the same job thousands of guys in mesh vests were doing years ago, and cheaper.