Learning to see and think about the lightness relationships in a picture is a very valuable skill for color photography which is easier to learn when trying to make black and white pictures because there are fewer distractions and fewer choices to make.
> I haven't seen any material since the digital age took over recommend that photographers start with B&W.
I am not super familiar with recent introductory photo courses/books/etc. Have you examined many of those?
While I haven't taken any formal classes in photography, I started learning around 2000 which is about the time digital started taking over. I started with film, then quickly moved to digital. None of the digital materials I used ever recommended starting with B&W. And the more formal classes I've looked at (but not taken) don't appear to start with B&W either. At the very least, they cover a lot of color stuff, where the older film classes only covered B&W, color was considered very advanced.
I honestly think B&W photography is actually harder than color when talking digital. That's because the scene you see has color in it, and it can be tough to imagine what shapes will be dominant when converted to B&W.
Actually, this was because developing color prints is orders of magnitude more difficult than B&W prints. Most of your famous early photographers are known for what they did in the dark room, not for their composition skills. E.g. you can buy an Ansel Adams poster for a few dollars, but an actual Ansel Adams print will run you several thousand.
I haven't seen any material since the digital age took over (sometime around 2000) recommend that photographers start with B&W.