Unfortunately one of the greatest weaknesses of FOSS is the lack of documentation and training. There’s lots of great training for Blender but as you’ve mentioned it’s mostly specific how-tos rather than more general understanding. Have a look at the credentials of the guy who developed that tutorial. No one with that experience is using Blender. I personally think it’s one of the biggest issues Blender needs to face to become mainstream.
The way I learned (am learning) uv unwrapping was to just sit down one saturday and start with a cube. I would play with different seams, different views, then I moved to a sphere, then to the monkey, then I started making shapes and playing with those.