SJ's are looking for a "help mate"
SP's are looking for a "play mate"
NF's are looking for a "soul mate"
NT's are looking for a "mind mate"
Someone who I can have a deep, thought-provoking conversation with (sometimes serious, other times light and funny but still witty) is such a fun and interesting thing to me. I asked my ISFP one time what would be her number one trait she would want in a partner and, true to form, she said, "Someone who makes me laugh a lot. Like all the time." It's just a matter of "different strokes for different folks". She always wanted to watch a movie that would make her laugh. I always wanted to watch a movie that would make me think.
As for F making a difference in assertiveness, doesn't F generally try to not offend people? It wants things to go smoothly between people. It doesn't want to step on people's toes. It would rather be diplomatic than abrupt. Whereas, T wants to speak the truth, whether it hurts people's feelings or not. If they can't handle the truth, then that's their problem, basically. These are very general statements and I'm sure someone will say, "Nuh uh, I'm an F and I don't care one bit about people's feelings." But, in a very general sense, I think this holds true.