That would be all fine and well if he didn't have the processing power of an Intel 4004 (the first microprocessor, 1971). That's something that can't be fixed no matter how hard he works. It's too bad, he's got a lot of other inherent traits like work ethic, clutch factor, accuracy throwing from different platforms, and running ability. I don't think his natural accuracy is bad, as much as his footwork and confidence are bad. Without the ability to process and trust what he sees on the field, he's doomed to the backup role. Without his overall talent, he would have been run off the football field by his second season.
People who are saying this makes Trubisky dumb are ignorant btw. There are people who are intelligent, but slow thinkers. Slow doesn't necessarily mean dumb. The problem is in the NFL you get 3 seconds to process the field once the ball is snapped, and if you can't quickly go through your reads while quickly interpreting what the defense is doing, you're going to pay at this level.
I really don't know why GMs don't factor in charisma when selecting a QB. Charisma relies on the ability to think fast. Trubisky has the charisma of a damp rag. Mahomes and Watson were far and away more charismatic than Trubisky, and look how it turned out.