Good work identifying the usefulness of Drop C tuning. C is used in plenty of bluegrass jams, called for by singers and guitarists. It was used by many professional banjoists in the late nineteenth century, partly because of its relaxed sound. When the tango and jazz fads hit and a loud instrument was needed, Drop C became the tuning of choice for banjo players playing that repertoire, which was often in C or F. (Guitar players who picked up the banjo for that purpose often chose Chicago tuning, like the top four strings of a guitar, and mandolin players chose the smaller tenor banjo, tuned like a mandola and instantly playable by mandolinists who needed more volume. It’s quite possible to use a five string as a plectrum banjo, using Drop C with the 5th string kept in G.
