The argument that diversity in a medium benefits fans is a pretty simple one, which can be made several ways. From one angle, it’s good to have a lot of series selling well because then the medium is safe financially if one superhit series ends. From another angle, it’s good to have a lot of series selling well because that means the industry can experiment more, finding the sweet spots of niches that might fall through the cracks if the industry was mostly dependent on 10 or so series earning 80 percent of the total income. I mean, it’s good to have those sort of “carry the team” hits, but an industry solely dependent on established blockbusters is going to be in trouble when the big guy’s fuel tank runs dry if they don’t have some sort of farm system in place to generate another crop of them.
When a market has strong diversity, one of the ways it manifests is in a rapid turnover rate in bestseller lists from week to week; series in the top 10 one week will be quickly pushed aside by new releases. Particularly in front-loaded markets (i.e. ones where the majority of sales take place over the first 2-3 weeks of release), it’s a very discouraging sign when a given week’s slate can’t even beat the runoff from last week’s. Since manga is a market where the thresholds for charting are ridiculously high and hard numbers are almost totally unavailable outside of Japan, this turnover rate is one of the few ways we can start to compare the two markets.