I tried to find the "every pass" videos from week 1 for Watson and Brady but couldn't find them, so my thoughts are merely anecdotal at this point. Even though the completion rate is similar, it just seems that Brady's passes are more often "on the money" than Watson's. One of the reasons that Hopkins often makes such crazy spectacular catches is because he has to adjust to less-than-accurate passes. If Brady completes a perfect pass exactly where it should have been thrown, and Watson completes a pass that made the receiver break stride and adjust, they both count the same in "completion percentage." I don't think that accuracy and completion percentage are an exact correlation.
I watched both games, and I have no doubt that Brady's placement of passes is better than Watson's. Texans receivers are often adjusting to where the pass is going, while Patriots receivers are often catching the ball in stride. Watch both games next week, keep an eye on the passes, and see which quarterback's passes are more consistently "on the money." On the other hand, perhaps my perception is completely off base.
Again, don't take me wrong, I am more than happy that Watson plays for the Texans. He is an exciting player and fun to watch, no doubt, and has Superbowl potential.