The question is whether the term equal is the right term in the first place. Is the President “equal” to the Vice President? As a human being, absolutely. In his function as Vice President, absolutely not. But like you said, if the President becomes incapacitated, the VP takes over his function
I do believe that a husband and wife are equal partners in the marriage with different roles. I don’t believe it’s like the pres./vice pres. kind of relationship where the vice president’s opinions hold little water and he’s basically just holds a lame duck kind of post.
A wife is not like that at all. She is actively involved in the family and marital affairs. Her opinion holds weight but that does not contradict the fact the the husband is the authority and the wife is generally submissive except when the need arises that she be assertive.