They can say it as much as they'd like. If they're going to treat us like children then we'll take our business elsewhere. If they can't be bothered to look through multiple threads then they are not suited for their jobs. This is the internet; you're going to have multiple threads made about things, particularly controversial things that are seen by a large portion of players as being "adversarial." You either accept that as a fact of life or you move on to another line of work.
But really, the biggest point against "only megathreads lead to changes" is the 1.0-to-2.0 transition in and of itself. There was nowhere near a single "megathread" and eventually we got 2.0 from it, and if they're just going to try and put things back in the box so to speak then that will blow up in their faces spectacularly. I know for a fact that I've got more experience and time put into this game than most of the community managers do. Many of them did not even exist during 1.0 while I was there since the first beta, giving feedback (polite, thought-out feedback, just so we're clear), testing the game from a variety of angles and so forth. I did the same thing when I was invited for alpha/beta testing of 2.0. I will continue to do the same thing here. If a new thread needs to be made, by myself or by someone else, then it will be made. If the community management team is incapable of accepting that feedback then that's on them. I am doing what I do for free, out of a love for the game. They are being paid for it.