You imply in your argument that finance mainly makes money from HFT("it's hard to me to see how market trading activity that provides a price for equities to the second") but this is simply not true, HFT and quants make up a very small portion of financial staff or profits.
My understanding is that the majority of big finance's income is from private equity or debt deals (pairing companies who need money with investors who have money), not from trading (there's very few people who we can confidently say are net winning traders and they don't scale).
No I didn't mean to draw attention to HFTs specifically, I understand they aren't big. I said 'second' instead of 'subsecond' because humans are also capable of reacting within seconds. But you are right that all those day traders losing money even things out and I was concentrating on the wrong thing. Investing and trading on longer time scales is certainly profitable.
My understanding is that the majority of big finance's income is from private equity or debt deals (pairing companies who need money with investors who have money), not from trading (there's very few people who we can confidently say are net winning traders and they don't scale).