It sort of works out correctly as I played 1000s of automatic spins on roulette and I saw my balance go down a little slower than the rakeback amount at some point. But nobody has discipline I guess because I always end up trying to win back and make profit
Brush up on your math because you are doing sums that don't make sense. If the house has a 2% HE and you get 10% RB, you don't have to do a simple subtraction. If it was that way, the house would lose money. As Saint-loup points out, the house gives you back the commissions paid, not the total. If it returned 100% of the commissions paid, the HE would be 0. Only if it returned 99% would it still have a small margin of HE left, which in this case would be 0.02%.