Stacked bar graphs, though a nice feature in packages, is distracting and not
meaningful, combined with the sales displaying all numbers you get very difficult to read graphs (see your haikyuu!! graph as an example, 34 tiny bars, numbers on every bar, multiple stacked bars, numbers on the axis, etc, Gintama is another). Week to week differences is better shown on line graphs, so it would be much better than doing everything as much as possible in a stacked bar.
Though I dont what the point of showing week to week data is because its so variable that you cant get meaning, in some case week two is large, some its small, its really not telling us anything about the sales trends of the manga. Example, the clearest one is Boruto, v1 and v2 had what seems to be large week twos, but then its smaller in the v3. Since we know its because of the number of days it was on sale, it seems there is no meaning youre getting from showing us it separated in weeks since the variable is the number of days it went on sale, not that more people rushed to buy it faster than usual. Further complicating things is, the individual stacks have no numbers, so were really just eyeballing slice size, which is easy when its just one or two colors, but 4+, combined with thin bars, and numbers, and so much other stuff, then yeah, distracting.