I agree with a lot of things. One of my students was an Open Water diver who purchased a BP wing right after OW certification and decided that he could "just dive with it." The wing was a small travel wing with around 20 lbs of lift and it was being used with a heavy steel plate, steel tanks and weights that were too heavy. Another one came to take a class with with D rings that were literally in the armpits and weight pockets had no stoppers so that would slide all the way to the front of the stomach.
With a recreational BCD, manufacturer has made a lot of decision for you. BP-wing requires a user who understands wing lift / buoyancy characteristics of different plates and tanks etc. At this point, there is no formal training that would take someone who is at Open Water level and give them enough know how where they can make educated and informed decisions about how to set a wing for their own diving needs.
I totally agree that GUE Fundies and UTD Essentials is not the only way. I teach BP wing set up to my students and I am not affiliated with either of those. These two courses were designed to take a recreational diver, who knows jackets and snorkel, and introduce them to a higher skill level with BP wing. So you have to imagine yourself as a fresh open water diver and with that level of knowledge you want to set up a BP wing that you acquired from ebay and are now making decisions. There is a learning curve after which these things become quite rewarding.