It's one of the few things in socionics which you can see in people's relationships pretty easily.
This is true, although I still think there is nuances and variations between types and people's preferences- and in @Braingel 's subtype system thing I am a pseudo-LII IEI so I like a mixture of aggression and caretaker-ness. With aggression still holding more weight but it's there. But I don't really want or need a partner as aggressive as my IEI sister does, for example.