You can go on Robinhood and buy stocks for free. Courtesy of some HFT in return for getting first dibs on your trades. If we compare that to the fees of yesteryear it's brought real value to long-term retail investors.

Unsophisticated investors only using market orders will also pay less spreads than they used to.

Going out on a limb, I think the losers are mutual funds and similar who are less able to monetize their fundamental analysis by buying or sell big chunks of stock without moving the market.