that may very well be really bad for consumers. If Robinhood sells to Citadel and Citadel has better execution than IB, you are getting worse prices on IB.
It does not work like this. You will always be crossed on NBB or NBA.
The concept of "bad" vs a national best bid or a national best ask can only come via order delay. Better execution via order delay as seen by a customer is always a lie as none of retail brokerages look at the order, look at the 100@101 x 100@101.1 market and say "ok, i'm buying 380K @ 101.09 from you" followed by posting the trade followed by trying to unwind position. Oh no, they simply present your order by adding it to the book.
No, that's incorrect. They can fill you better than NBBO if they have an internal prediction that NBBO is moving. Or they can fill your sell order at better than bid price, to be more precise.
The concept of "bad" vs a national best bid or a national best ask can only come via order delay. Better execution via order delay as seen by a customer is always a lie as none of retail brokerages look at the order, look at the 100@101 x 100@101.1 market and say "ok, i'm buying 380K @ 101.09 from you" followed by posting the trade followed by trying to unwind position. Oh no, they simply present your order by adding it to the book.