Ok fair enough, but I don't really see any evidence of slow processing. Especially after his rookie year when he ran a real system.
His rookie year he essentially ran the Clemson offense with OB's terminology - He was reading only half the field in college and that was what he was doing for the most part in year one.
Also teams didn't have tape on him , they hadn't figured him out - Carolina laid the blueprint for beating him last year and several teams followed their lead - Denver , Buffalo and Baltimore did it best. They didn't over pursue or run their wide rushers out the back door allowing Watson the edge , rather they kept him in the pocket and forced him to make decisions from there while pressing the middle. Buffalo made one mistake and it cost them that game - They almost won with their own QB sucking the wind out of their sails.
Once teams figure out a QB they have to adapt and show they can beat them other ways. Watson hasn't had a really good game since week 9 beating Jax 26-3.
They damn near let Tampa Bay sneak away with a win with Winston throwing 4 picks.
No one is saying he's stupid , what they are saying is that either he doesn't see things well or he isn't processing what he sees fast enough.
I lean towards it being a little bit of both having watched every game in the All-22. I see him missing or overlooking what should be easy throws time and again.
Then there's Watson himself playing speed chess in an attempt to help him make quicker decisions. I don't think he does this unless he realizes its something he needs to improve upon.
Thing is , speed chess is more about memory than calculation , particularly once you get beyond the opening book moves - I've been in this situation before / seen something similar and X was the right response.
I started playing chess before I could walk and had a GM rating in postal play , a near GM rating in OTB tournament (90/40) play and won a USCF sanctioned blindfold tournament that had multiple GM entry's , I was utterly terrible at blitz chess .... not having time to calculate things out to an end.
More often than not blitz chess is chock full of mistakes that would be taken advantage of in longer time allowances , even by lesser players.
Maybe it helps him in that he's recalling information more quickly - Things he's seen before and able to react accordingly.