I only agree with that in the sense that I think Facebook (the facebnook.com site) usage will decline quicker that Reddit usage. As someone who's been on Reddit for almost 9 years, I feel like the redesign is kind of equivalent to the timeline change that Facebook had. While it's not going to cause massive user drop off on it's own, it's kind of the thing that opened people's eyes to the fact that they are the product on Reddit. Every new complaint about Reddit will be, "First they did the redesign and now they are doing {insert new annoying thing}"
I think we'll see a gradual decline in Reddit usage for a while, but nothing major as there are no real competitors in the space that can handle anywhere near their scale. Once an actual competitor pops up though, all it's going to take is one or two missteps and people will start moving off Reddit.