I think there's an underlying problem that 4e can't escape: Even if it's not true that 4e is a "failure" the fact that there is a widespread perception that it failed is going to taint its reputation going forward even if it's true that there is an equal or near equal proportion of gamers that like it compared to 3.x/Pathfinder.
This isn't 4e's fault, and it's not the fault of the players who love the game. Ultimately it's WotC's fault for failing to manage perceptions in the run-up to the launch, and failing to maintain dominance in the industry in the wake of the release of Pathfinder.
So we spend a lot of time arguing about what's selling more and how many people are playing, usually inferring from some subset of data that we happen to have access to. But the fact that the entire conversation revolves around the question of whether 4e was or was not a failure means that, as far as it's perception in the public realm goes, it's going to be seen as a failure.