They are bleeding you for less each turn. Not only must a vampire be untapped, but unless it has superior dominate, it is tapped. Thus it can only stop one incoming attack. Finally, the vampire has to actually block the attempted attack. Putting in the Obediences will only facilitate matters.
Obedience is good, but against a well designed combat deck, more than obedience is needed.
Obedience will not shut a combat deck down. No other answers were really given to combat defense. The problem is, that in doing so, it waters down its main focus. That is its biggest weakness. Combat's methods of dealing with bleeders and voters is effectively its own main strategy.