Since the dots in btop's rendering are using the Braille characters, meaning you get six dots in the space that would be taken up by one alphanumeric character, the resolution on those dots is surprisingly high. A maximized terminal on my screen is size 316x86, so that's 316×2 x 86×3 = 632x258 of "Braille dot resolution" (a term I just made up) available for the graphs. Sure, that's lower than the 2560x1600 pixel resolution of my screen, but you're entirely right to ask "Does that really matter?" The graph would be smoother with about 4x more horizontal pixels and 6x more vertical pixels to work with, but I doubt I would glean any more information at first glance.