Matt Levine has some insight on this [1]. And you're right, Robinhood's price improvement was bad compared to standard brokers:
> By March 2019, Robinhood had conducted a more extensive internal analysis, which showed that its execution quality and price improvement metrics were substantially worse than other retail broker-dealers in many respects, including the percentage of orders that received price improvement and the amount of price improvement, measured on a per order, per share, and per dollar traded basis.
But again, it's a relative issue. For small trades, overall you got a better deal than paying a slightly better price plus a fixed commission. For large trades, nope. So, at Robinhood the rich big traders subsidised the smaller ones. Kind of fitting for the name.
> For most orders of more than 100 shares, the analysis concluded that Robinhood customers would be better off trading at another broker-dealer because the additional price improvement that such orders would receive at other broker-dealers would likely exceed the approximately $5 per-order commission costs that those broker-dealers were then charging.
All in all, I think their model is defensible, but lying about it isn't.
ETA: To be clear, I think their pricing and revenue model is defensible. But: a 10$ fee for a long term trade is also pretty negligible. What Robinhood have democratised is day trading and gambling, and that's not good.
[1] scroll down to "Robinhood (1)": https://www.bloomberg.com/opinion/articles/2021-01-07/the-ip...