That may have been the case in 1945, but a lot has happened since then.

Honestly, as soon as those interested in music started to categorize music in regards to a particular band (or instrumentation of the band) instead of the structure of the music itself, you start to see things fall apart. Jigs, reels, polkas, waltzes can all be played on any instrument. How do you define "alternative music" or "folk" Or "bluegrass" or "alternative rock?" When you categorize a band instead of a song, when the band plays a completely different style of a song, do you still force the category into what you lumped them into?

Then you fall into the difficulties that all those that classify things fall into. Are you a splitter or a grouper? The more you know about a topic, the more you are able to split something up. You talk about bluegrass being easy to define as compared to old-time styles. But to me, there are huge differences in three-finger banjo picking with metal finger picks and a thumb pick? The approach Ralph Stanley uses to play the banjo is completely different from Don Reno. Which is different from Bobby Thompson. Which is different from Bill Keith. Which is different from Earl Scruggs. Which is different from Noam Pikelny, Ryan Cavanaugh, Jens Kruger, Jayme Stone, etc, etc, etc. Heck, the approach Bela Fleck plays the banjo with The Flecktones is completely different than the approach he takes when playing with his wife. Or even from song to song.

I am of the personal opinion that genres are useful to lump broad categories of music and bands to help lead people in the right direction (if you like this... then you may like the following, which fit into a similar vein of music). If you like more "traditional" bluegrass, then I can rattle off a number of bands you would enjoy. If you like "Nashgrass" bands, that would be a completely different group. Or the "California" style of playing. Or "contemporary acoustic" or "jam grass. And if you like the general sound of bands like The Punch Brothers, Cadillac Sky, Steeldrivers, I would lead you to a thumb pick with two metal finger picks, and teach two rolls (forward backward roll and alternating thumb). MUCH later on I would talk about Noam's approach compared to Matt's approach compared to Richard Bailey, and what makes them sound the same and what makes them sound different.

But the thing is... to the vast majority of people, a banjo is a banjo. Even to those who may know the instrument, a thumb pick and two metal finger picks played in a syncopated pattern is "bluegrass banjo." And if you have a guitar, banjo, mandolin and bass in your band, you're a bluegrass band. And it's easier, especially when people are starting, to start off slow and develop that knowledge and awareness of everything the banjo world has to offer. And that's the tough balance.

There are going to be gray areas. There are going to be the outliers, the historically significant players, the ones behind the scenes who influenced those who got all the attention. The unique, subtle and not-so subtle differences between banjos players that put them into sub-sub-sub categories. But in my generation, the vast majority of people got into banjo because of The Beverly Hillbillies, Deliverance and Hee Haw. Similar that people get into banjo today because of bands like The Avett Brothers, The Devil Makes Three, Trample By Turtles and Old Crow Medicine Show. Heck, the Pete Seeger book taught basically two right-hand techniques, and look at how influential that books was for many banjo players.