I looked at the same video, and I see the scrolling is moderately smooth (not really smooth - I notice but some people can't see the difference in games, so the same would apply).

But the complaints about slow drawing of browser content are crystal clear in the video. Much of the time, when scrolling at speed all you can see is a blue display - you can't tell where you are in the page. And then it eventually draws itself in, sometimes in several stages, almost like loading a web page (although it's clearly just rendering, not fetching or layout).

That can be improved in software I'm sure. (Very sure). But whether it will actually be improved remains to be seen.

Having seen that video, I'm confident that it at least some browser canvas implementation is likely to fix the rendering performance, even if it's not in the shipping browser. E.g. Tear or Fennec, for example?