Trust me, the difference between the comments vertically scrolling in the sidebar and horizontally on top of the video is huge. In Twitch, when the comments become fast enough they literally give no time for the viewer to parse and understand most of them; With bullet comments plus Asian languages that have high letter-to-meaning ratio (or at least with my experience with Japanese on Niconico), each of the comments horizontally scrolling on top of the video leave just enough mental processing time to read through the majority of them and to grasp the atmosphere of the commenting hive-mind more clearly. This creates a sense of togetherness that is much more tight-knit than what you get from Twitch comments.