OP I think I agree with some of your points, but also feel lost on what you're trying to get to reading your first and last post. Marketing wise someone could probably write a 100 page dissertation, but I think bass performance boils down to cabinet size and competing at a price point. I've tried to give away great speakers and they've been vetoed because of being too big - even lil floorstanders with dual 8's.
I agree it's not rocket science. I have some great speakers that can do bass solid for most music. Frankly I'm blown away by them for price and performance and that's why they're keepers. For true 20 Hz and below performance I needed to add a sub. It's pretty tough to compete with a good sub for that last bit of low extension with the dedicated high power amplification and cabinet size. I prefer to cross at about 30 Hz with my mains having solid performance down to there though I understand the 80 Hz method.
I have had some pretty big speakers that had stupendous bass, but I couldn't control it in my room. This is the other advantage of subwoofers though you could also use DSP etc to tame powerful speakers. As someone else stated multiple subwoofers can be used for room issues to get ideal bass response throughout. I will be going to 2 subs when I can fit them, but have heard of many going to 4 for most even response.
I love 2 channel, but a lot of the "full range" speakers I would love to have at my price range and far beyond that don't dig down to 20 Hz or below. I listed some very expensive speakers that do go below 20 Hz on another site and was chastised as being a snob for providing them as good examples. I think it's all about building the best system you can afford in your space for your tastes, but it sometimes seems to get way overcomplicated.