This is not correct. Firms don't buy order flow from Robinhood in order to trade in front of those orders, they buy order flow from Robinhood to execute those

This is not correct. Firms don't buy order flow from Robinhood in order to trade in front of those orders, they buy order flow from Robinhood to execute those orders for those customers which is a service that those customers pay for as purchasers of liquidity.