Lawrence, Bryce Young, etc all have better/higher pure football physical traits, some by far. Some also read the field really well and/or are continuing to develop in that area.
I'm a huge Brock homer, but you have to realize a not insignificant portion of his success is because of the system. But that isn't meant to take anything away from him as that's part of the magic to building a great team - finding the right players for the right positions for the right play calling. It's why TJ has been successful at Iowa State - he can take a guy like Brockington, put him in a different system, and make him thrive.
I don't think many people would argue that Purdy would be doing as well as he is if you put him on the Jags, Bears, or Tampa Bay rosters.
But as long as the system he's in is built around managing the game, reading the defenses, taking what you can get, not turning the ball over, and making the occasional long throws... he's going to look pretty damn good - because he is at those exact things.