Your assumption that it is the motivation for most end-game players requires a narrow and almost tautological definition of end game players and has no empirical backing. There is a large number of end-game players that get gear on the basis of enjoyment rather than maximum utility. In fact, Alla and BG Media corroborate that notion quite nicely. He's not saying everyone should unsubscribe until 99. He's saying that the nature of the level cap adjustments, something that ceases at 99 (Which is why your subsequent point is false as well), renders most gear obsolete within the next two updates. While this statement is questionable, if it is true, it does not necessarily follow that gear will be replaced as rapidly once the level cap reaches 99.
If you wanted to make a smart rebuttal, you would have mentioned that it takes gear to make gear. The implication being that an army of gearless people is incapable of defeating certain enemies. Another point would be that a lot of AF3+2 gear is specialized gear, and because of that, is difficult to replace compared to stat gear. For example, DRG AF3+2 hands have Enhancing spirit link. So does DRG AF+1 helm. These are pieces unlikely to be replaced because they perform specific utilities.
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