Too much is put on his shoulders. When you score what should be the game winning drive and the defense gives the game away or you spot the other team to TDs off the back and you are constantly playing catch up, that is a lot of pressure in a young QB. I think a big part of the problem is Watson tries to do too much and the offense has to abandon the game plan early because the defense can't stop the other team.
I am not saying Watson doesn't need to improve, but the situation is magnified because of the situations he is put in. It is also hard to establish a rhythm when the other team keeps marching down the field, scoring points and running the clock. I don't think the play calling helps him out enough, but I believe part if that has been Watson being over committed to the big play and not taking (or possibly seeing) the underneath routes and checkdowns.
I know you don't believe this, but I think we have a QB to get us to and win a SB. I don't think he is that QB yet, but I think he definetly has the potential to become that QB. Regardless, one player doesn't win a SB, it takes a team (players and coaches) and we ain't there, yet.