I actually don't think you are meant to relate Brad's 4 roles to the natural positions. The point of his descriptions is a role that they play. For example Simmons would be a ball handler even though he is a 4. JJ is a swing because he is able to guard multiple positions and stretch a big out to the 3 point line. I don't think you can say "a swing is a guy that can play the 3 and 4" or "a wing plays the 2 or 3" because the whole idea of Brad's roles is to move away from the idea of positions
Yes you can say that a swing is a guy that plays 3 and 4 cause that's exactly what Steven's said.
And Simmons would either be a big or a swing that can play Point forward. Simmons is a PF in my mind that can handle and create.
Simmons is 100% a ball handler. He is not a swing. This is my point, you are trying to directly translate from one form to the other. If that were possible why not just stick with 1-5?
The system that Stevens talks about is based around the skills that the players have and less about their size or weight. Avery Bradley has the size of a traditional point guard but he is classed as a wing by Brad because he has the skills of a wing. Simmons has the skills of a ball handler primarily
Simmons will handle the ball no doubt. Is he guarding Ball handlers? Absolutely not. You have to look at it that way too. Right now I don't know who he can guard besides a 4 or 5.