Eh, my wife and I have very different personalities (I'm an introvert that LARP's at being an extrovert out of necessity at times, she's genuinely outgoing and social) but
There is a LOT we differ on in terms of hobbies, people (I dislike people, generally), personality (I'm obsessive and logical to a fault, she's emotionally-driven but always willing to re-evaluate her position based on evidence, even though she tells you she isn't), organization (ADHD brain, I have "organized clutter", which drives her nuts), money (I manage it, she doesn't want to think about it), entertainment (we watch very different things), music (we listen to completely different genres)...etc.
I also have a tremendous amount of respect for her brutal honesty and fierce loyalty, always knowing where you stand with somebody who will never play games or not tell you exactly how they feel, for somebody with my personality, I can't express how much of a stress avoidance that is.
People are complex chemistry. Trying to distill it down to two possibilities (opposites attract or only like personalities will persist) isn't possible.