That smaller screen on iPhone X has 2436x1125 resolution, which is only 33% less pixels than my desktop monitor (which is 2560x1440). Considering that the vide

That smaller screen on iPhone X has 2436x1125 resolution, which is only 33% less pixels than my desktop monitor (which is 2560x1440). Considering that the video plays full screen on the phone, and in a much smaller window on my desktop system, the inferior GPU can render that much more smoother than the desktop, which shows that GPU is not the problem here. Also, grabbing the scrollbar on Firefox Linux restores the smoothness, supporting "tick" theory.