>be specific about classical (pre-1950), jazz (pre-1980), and
>electronic music (up until a few years ago perhaps): who are
>the equally or more popular mediocre talents i might be
>overlooking?

It is appropriate of you to call me out on it, but I must plea cop that my knowledge isn't deep enough of the other genre to provide too specific data. The idea seems to have been consistent enough in my own lifetime that I have no reason to assume otherwise about the past. I have generalized impressions of the popularity of certain Big Band leaders extending into then-contemporary biographical features (Glenn Miller, Gene Krupa) but not to others who are historically provided with greater esteem (Ellington, Basie). It is not meant to imply that Miller and Krupa are not skilled, but we generally would agree that Ellington and Basie are more significant in influence. Social and institutional factors obviously play into those examples, as to why some would be deemed more commercially viable than others, but I assume that there are always social and institutional factors that result in the popularity of some at the expense of the innovators.

With regards to electronic music, the examples that come to mind are those like Fatboy Slim or Prodigy, that despite their greater contemporary popularity have not held as much historical esteem in succeeding years and more innovative/influential peers like Aphex Twin.

EDIT: I am not necessarily saying that the innovators or the influential are not popular at all, more that contemporaneously they may stand out with less relief from a mainstream perspective.