I have no issue recognizing the feedback loop, but the statement was extremely strong to me, and I don't think the feedback was that strong an impact. Valuable, yes, beneficial, yes, but the main reason for 5e's success? Eh. I think it would have done pretty much the same with the first playtest packet released, honestly. 5e's success as a system isn't really owed to the public playtesting. 5e's success with regards to making fans feel involved, though -- that's the real kicker to the playtesting: it gives fans a sense of investment and goodwill, even if they offer little say in design.