There are various equivocal hypotheses pros and cons, but the only one that matters is how the speakers actually sound.
Agreed. I was responding to a proposed model ("towers are bookshelves with attached subs") with another model ("no they are not; at least not in light of 3-way towers vs 2-way bookshelves")
Here's another hypothesis. I bet if Harman conducted a DBT using completely untrained randomized audiophiles w/ towers 2.0 (lesser bass) vs monitors + subs 2.2 (better bass), most people would prefer monitors + subs because the later has better bass.
Back to hypothesis 1 problem. Little computer speakers plus awesome sub vs B&W N800's with (slightly less) sub.
Result: In the real world individual speakers and setups must be evaluated individually.
Certainly not every monitors + subs 2.2 system sounds better than every towers 2.0 system.
I never advocated for 2.0. Indeed: I never would suggest not using a sub except (and even then only maybe) with some extreme mains.
What I actually discussed was the difference between a 2-way + sub and a 3-way (the person I responded to had described them as functionally identical).
Which is better? Well: 3-way+sub; but then go back to hypothesis 1 that every speaker needs to be evaluated individually.
For some perspective:
My bedroom mains are 2-way TL towers and the surrounds are 3-way towers all with subs
My family room alternates between 3-way TL towers and 4-way towers. No subs at present, but want some.
My computer is 2-way bookshelves with a sub.
And so on and so forth. I'm not really even trying to argue one in favor of another: just point out that they are not the same thing.