What does this mean? How can a franchise that has not yet released its first sequel "prove" that it has no staying power? If the first sequel brings in $1.5B, wouldn't you have to retract that statement? If the attractions at WDW become the hardest FPs to get, doesn't that statement become false? It is very clear that Disney fan boys and fan girls who post here are not the same crowd who post on Avatar chat boards. But that in no way "proves" that the Avatar franchise has lost its staying power. Now, if the first sequel flops, then one can proclaim that the franchise is dead. Remember that almost 2 decades elapsed between the third and fourth Star Wars movie. And 14 years elapsed in between the third and fourth Jurassic Park movies. But the fans came back. The gap in time between 2009 and 2017 pales in comparison. We simply aren't at the point yet where we can drive a stake through the heart of this franchise.
No matter how it is sliced or spun, Avatar is #1 in actual worldwide revenue and #2 in adjusted worldwide revenue behind Gone With The Wind, but only after taking into account many theatrical re-releases which Avatar cannot replicate. (Though I would not be surprised to see a re-release prior to the sequel.)
As noted above, the number 14 is domestic only which in a global economy, is meaningless. There is no metric that can be used that places Avatar any lower than #2 in terms of worldwide success.