A view commonly expressed on this forum.... I just can't agree. I think it actually rises to one of the big misconceptions on this forum.
What I think is true is that if we know someone only from his/her work, we could easily get confused between types within a certain quadra.
But duals are not almost the same. They're both really confident at what the other is not confident (or is even downright terrible) at. That's a big difference.