I don't think there is confusion over the approach. I think that, in the general way you've described, it's understood. The particulars of how it is achieved seem to vary pretty significantly among the posters you've listed, so I think some confusion may come from there.
I also think, there's some confusion about resistance to not simply discussion of potential drawbacks or failings of this approach, but the very idea that such failings could even exist.
For instance, based just on your description, I would be concerned that authoring such details along the way may not allow for as detailed a story. I would expect that, compared to a story authored beforehand, that one authored on the fly would possibly lack verisimilitude.
This is certainly a failing I've seen in games where I have relied almost entirely upon improv rather than pre-authored details.
I will try to explain my own resistance. The implication is that there is something wrong with the approach or a given game design rather than it simply not being suited to a particular set of player motivations, risk tolerances, and cultural values. I would rather not make evaluative judgments based on what I feel other people might perceive to be failings. The problem with that sort of analysis is that it involves merely guessing what other people could possibly value. I can only meaningfully speak to my own interests, values, experiences, and knowledge.
Part of the reason why I prefer to speak in terms of suitability, risks, and pain points is that there is no implication that we must do something about them. Often the specific pain points and risks involved with a given design are necessary to achieve some other result that we value. Additionally a pain point might be there by design in order to spur a player to action or act as a meaningful consequence for unskilled play. It sucks when you cannot play a particular character anymore, but you have learned lessons along the way that will result in a more rewarding experience in the future. Rewarding play is dependent on well considered risks. What happens when we mitigate risks is we remove the possibility for dramatic failure, but also the great rewards that come along with social, creative, and strategic risk taking. We can consider which pain points we are willing to experience and risks we are willing to take to get what we want out of play rather than assume some failing.
There is also the element where I would prefer not to do anything which would push this discussion more into the realm of debate rather than the realm of analysis and criticism. I am somewhat concerned about providing rhetorical weapons that could be used to cut off discussion rather than enliven it.
Essentially we are talking about matters of perspective here.
I do not view it as a failing of my most preferred approach that active and vigorous collaboration can sometimes fall flat or result in narratives we might not be particularly pleased with. These potential pain points and the creative risks involved are necessary to experience these deeply personal stories and the experience of achieving creative success together and to learn how to best collaborate in the future. It might not be what someone who is not me wants out of their play, but that is neither here nor there.
I also do not view a tendency towards illusionism as a drawback outside the particular context of my own desires. It cuts against my particular interests, but that says nothing meaningful about the interests of the people who want to play that sort of game. Just because a given design, approach, or set of techniques happens to not coincide with my own motivations and cultural values does not mean there is something wrong with it.
Aside: I strongly disagree that a more improvisational and collaborative approach will necessarily lead to a less meaningful sense of being there in the moment and reduced coherency. That very much depends on the actual techniques and drives involved in making those decisions. I find that when I engage in copious prep of the type recommended by most mainstream texts the resulting experience is less organic, feels less genuine, depends too much on contrivance and lacks authenticity. I find when I put less emphasis on designing everything and let go, depend on the other players, and approach things with discipline during play I feel much more connected to the fiction.
