This post does a good job of explaining what I see:
...there is no such thing as degrees of possession. Either one does, both do, or neither does. And as far as any person can tell, "both do" is the only conclusion you can come to with any degree of certainty.
Whether Jennings had more possession in the air or not is irrelevant. There is no such thing as possession in the air. Possession inherently implies two feet, a butt, a shoulder, and elbow, a knee, a hip, some body part touching the ground. At the point when it most mattered, when both players hit the ground, both players had an all but equal claim to the ball. Any rolling or twisting or manhandling afterwards is pointless. Once both players hit the ground in a state of dual possession, the play is dead and it's a touchdown.
There are very reasonable arguments to be made that it was an interception. When you break it down and go frame by frame, it looks like Jennings probably has more of a claim to it on the ground. Unfortunately, the official whose call it was to make didn't have the luxury of breaking it down frame by frame. He had to make the bang-bang call as he was watching six players go up and come down, all clawing at the ball. It looked to him like it was dual possession as they came down...
I can see how people can call that an interception, but I cannot see how you can make the claim that Tate had absolutely no possession of the ball at that point.
By the reasoning in the post above and by yours, all a receiver need do is have his two hands touching a football which is in "possession" of a player who has intercepted the pass and has both feet on the ground -- by "possession", I mean two hands on the ball and the ball pinned to the body -- in order to claim a "simultaneous catch" and retain possession of the ball.
If I were a receiver coach, I would tell all my guys, "look if you see the defender has intercepted the ball, just go touch the football with both hands if you can and you should get the benefit of the doubt".
The play last night sets a real dangerous precedent.