I disagree with your comments regarding Watson not hitting receivers in stride and a lot of his throws are low. When it comes to accuracy, Watson can improve and become more consistent. Will Fuller is one of the fastest WRs in the NFL. He's not running too many short hooks or out and Watson hits him in stride consistently.
I tend to look at a QB's footwork in the pocket. Watching Watson, when he releases the ball on time, at the top of his drops or when he makes quick decisions or when he knows based on pre or post snap where he's going with the ball, he is very accurate.
However, when he gets sloppy with his footwork, throwing off balance, holding on to the ball waiting to determine if he and the WR are on the same page, the pass rush is bothering him or waiting too long before looking for his check down, his accuracy suffers. So, I don't think he's consistently inaccurate. However, you will see great throws then out of no where a "how did you miss that throw" play. That is where he needs to improve.