I'm not sure I see more than a third-string hustle guy in Watson tbh. In particular I was a little disappointed by his footspeed in the summer league. Guards were running right past him in a straight line to the rim, which isn't a promising indicator of his ability to switch at the NBA level.
He has some game, especially if that corner three ball continues to develop. I like the court awareness and unselfishness. Let's pump the brakes on the Al Horford talk though. In all likelihood that's several rungs too far up the ladder for Watson.