Was cruising the internet and came across this.
https://www.scribd.com/documen...l-Railroader-1940-06
Article titled HO Gauge Continues Rise caught my attention. I had been under the assumption that the rise of HO was Post WW2. Clearly it was well on its way to dominance in the Model Railroad portion of the Hobby earlier than that. The survey does include 3 Rail but, these Polls were from the magazine's readers, so probably doesn't really capture the size of the "toy train market." Also doesn't breakdown if 3rd rail was outside or center rail? Of course even then there were Scale 3R Modelers and the "Traditional" People.
Anyhow thought it was interesting.
BTW other interesting things in the magazine, including prices in ads. Adjusted for inflation the current prices we pay aren't that bad.