ubiq: Why would you say it doesn’t hold water? Shulchan Aruch paskens that a wife is exempt from Kibud Av V’Eim, which is not only a m’doraisa but is actually one of the Aseres Hadibros!, due to her obligations of serving her husband exempts her from her father and mother.
According to your line of thought, you should argue that she should still be chayiv in Kibud Av V’Eim when she isn’t serving her husband. Yet the Halacha is that she’s not.
(The husband’s obligations of Kibud Av V’Eim precedes his obligations to his wife.)