Yes, but I think you're downplaying the importance of that.
Two people can be completely the same in all the right ways (beliefs, goals, etc), but if they aren't able to click in the way duality is supposed to then it's not going to be as good as it would seem it should.
On the flip side, if duals are different in many ways and the people haven't become closed to other ways of doing/seeing things, then the relationship can prove to be enlightening in more than just socionic-related ways.