As someone who values seat width over seat pitch - mostly due to shoulders, although my middle section is doing a great job of catching up over the years! I can confirm that the seats in row 22 AND row 9 are narrower than any other seats on the plane.

US used to charge more for these. I always felt bad when I saw another guy my size presumably have to pay for the privilege of squeezing into one of these torture devices. I avoid those two rows at all costs.

Personally, I prefer all Arbii to Boeings in Y - the seats are about 1" wider. Makes a big difference to the back and shoulders to me. (please don't hate me for saying that!)

On a related note - EVERY seat on Southwest is completely intolerable for me. I won't fly them if I can avoid it, and even if I have to, < 2 hours flights.