Unless the ref also ruled GTTG and didn't see the ball hit the ground which would be overturned on replay which it was. The ball would also be at the 1. You said if GTTG was ruled then it should have been a touchdown after Dez finally established possession in the endzone. Those are bobble/rollover yards allowing you to advance the ball after you were touched by a defender and hit the ground yourself. Literally not a rule with GTTG or anyplace else. Show me where it is in the 2014 rules.
If the ref did not see the ball hit the ground then it is a touchdown because there was no possession until he was in the endzone, by that logic. Bobble rollover yards isn't a rule? What are you even talking about lol? There's nothing that says "a bobbled pass can't be advanced," which is what you're claiming. A player isn't down until they have possession and the spot of the the ball isn't determined until a catch isn't complete. A player can lay on they're back and bobble the ball 100 yards forward if they want.
A player can't be ruled down down by contact if they do not become a runner, and a player can't become a runner without completing a catch first. Again, there are two ways the ref can rule assuming, as you're claiming, that they did not see the ball hit the ground:
1. Down by contact at the half yardline. This means that the ball was possessed, the receiver became a runner, and was touched down. The ball moving after the fact is irrelevant.
2. Touchdown. Possession was not complete when the runner was down before the goalline, so the player was not down by contact before the endzone.
If the ref did see the ball hit the ground:
1. Down by contact at the half yardline. This means that the ball was possessed, the receiver became a runner, and was touched down. The ball moving after the fact is irrelevant.
2. Incomplete. Ball hit the ground and came loose.
In either instance, the ref ruled that the receiver was down by contact at the half yard line. Because of that, these things have to be true:
1. Possession was determined
before the player reached for the goalline.
2. The player is down by contact
before the ball comes lose.
3. GTTB is irrelevant, because possession is determined
before the player makes the action that caused the ball to touch the ground.
As such, the only way to overturn the call is to determine that the player had not established possession before reaching for the goalline. However, possession is determined by the fact that the player is making a football move because they are diving/reaching for the pilon as a runner. You can't overturn that as there is not "indisputable evidence" saying otherwise, because it is a subjective call. There is no way to determine, in an indisputable way, that a player was falling, rather than diving/reaching.
They messed up the call. It is what it is.