There’s two significant differences between the Ertz play and the Dez play. The first big difference is that Dez was battling a defender on a 50-50 jump ball where he had to leap and high point the football to win the battle. He never had complete control of the ball until it reached his shoulders and by that time his momentum/body lean was taking him to the ground requiring him to hang onto the ball through the contact of the ground. Ertz was not battling for the ball and his feet never left the ground.
He maintained firm footing, caught the ball and turned up field instantly becoming a runner. Once he established himself as a runner it was a catch, therefore he didn’t have to complete the process of the ball surviving the ground. Anyone who can’t see the differences in these two plays is a brick wall and a waste of time trying to have an intelligent football discussion with.
You are correct, the Dez and Ertz plays have similarity, but are not exact. However, that doesn't negate the fact that the decision on Dez was not based on fact, but OPINION. Yes, the FACT is that Dez lost the ball when he contacted the ground; however, the ground contact aspect of the rule is only pertinent IF the receiver has not performed a football move prior. The 2014 rule doesn't say football move or, as you say, "become a runner"; what it actually says is:
"maintains control of the ball long enough, after (a) and (b) have been fulfilled, to enable him to perform any act common to the game (i.e., maintaining control long enough to pitch it, pass it, advance with it, or avoid or ward off an opponent, etc.)."
The overturn of Dez's catch hinges on whether he was trying to "advance with it" or something else under the "etc." In my opinion, he was attempting to advance by stretching to attempt to score. The on-field official at the point of the catch with an unobstructed view obviously thought he did because he ruled it a catch. The replay officials didn't think he did, therefore, it was a no catch. Those are differences of OPINIONS, not fact or irrefutable so the ruling on the field should've stood, not confirmed, but stood as called. Since it was called a catch, it should've stayed a catch. If the on-field official had ruled it incomplete, it should've stayed as incomplete.
Non-catch proponents base their case on that what Dez did wasn't a
football move. Catch proponents base their case on it being a
football move. There are a cross-section of NFL fans, media and players on each side so what you have is a decision based on OPINION rather than irrefutable fact. So what is deemed "an act common to the game" falls under the Potter Stewart definition - I can't define what a catch is, but I know it when I see it. That's clearly not fact nor irrefutable evidence so the call on the field should've stood. Anybody that can't see that is a brick and there's no use in having an intelligent football conversation with them.
By the way, the Jesse James play had elements of Dez's play but was more like Ertz's. IMO, Jesse James caught the ball, but again, that an OPINION..