Until both the defenders feet touch the ground he has not gained control. Here is a pic from a different angle:
Both of Tates feet are down and he is clearly doing more than just touching the ball.
That's different from catching the ball at the same time and showing that he had control.
That's what the picture shows.
You are confusing gaining control, simultaneously catching and retaining control.
The person catching the ball must gain control (catch the ball) and retain control (keep the ball) all the way to the ground for it to be called a reception or interceptioon. That’s the gain and retain part. Gain happens first - that is what must be simultaneous. Retain is what happens next, and they both must retain simultaneous possession - THEN the rule comes into play.
If a player gains control of (catches) the ball, but is hit and loses the ball before coming down, it is ruled incomplete. You’re statement that he can’t gain control until both feet touch the ground is just false. He must RETAIN control until such time as he touches the ground for it to be ruled a completion (or interception). But the simultaneous possession rule talks about GAINING control at the same time. If the rule meant what you say it means, it would talk about GAINING control, and another player holding or touching the ball SUBSEQUENT to the initial catch and BEFORE hitting the ground. That’s not how it is stated. It is stated as catching simultaneously and both retaining control.
Once a player gains control of (catches) the ball, another player must clearly take possession AWAY from the first player to possess it - regardless of how possession was gained in the first place.
Simultaneous possession ONLY apples when both players CATCH the ball at the same time.
Here is what happened:
Defender CATCHES the ball.
Defender pulls the ball into his body
Receiver gets his hands on the ball after the defender has caught and pulled the ball into his body (simultaneous possession rule does not apply).
Defender keeps the ball held to his body as he hits the ground. (Receiver did NOT establish possession by TAKING the ball away from the defender - remember, simultaneous possession rule does not apply)
The official calling touchdown blew the call.
The replay officials could not (by rule, as I understand it) overturn the possession ruling - which was clearly incorrect.