I think it's possible that someone with well-developed functions would fall in love less easily because they wouldn't need someone as much. In other words, they wouldn't fall in love necessarily because they need to feel loved or appreciated, like many people do, but rather because they want a relationship with the other person. In other words, they don't fall in love with love, but love with the Other. At least, that's a theory.
However, I think that more people tend to fall in love with someone who is well-rounded because they have a higher likelihood of seeing some aspect the are attracted to in that person, especially if that person is kind and open. Sometimes a well-rounded person is more intimidating and strong, but even that often creates admiration.
The thing about the counterpart relationship is that it does create a strongly passionate relationship, but it seems to die as the passion dies. Real, lasting love is not greatly passionate; it is calm, appreciative, and nurturing rather than emotional and turbulent. So, in my opinion, it is better to find someone who you can relate to on an un-romantic as well as romantic level because those are the people you'll be able to stand once the passion begins to level out.