I don't understand why you are assuming that the author does not correctly understand the fictional positioning that they themselves have established for the very purpose of this exercise. In addition, I think it's important to note that the rules do not call for "the" best outcome, merely "a" best outcome.
I think I explained that. Note very carefully the bias the author has on the fictional positioning of Pietro the stable boy in the parallel examples of A and B. In the first, the best outcome involves the stable boy's meekness turning the hearts of the bravos in his favor. And OK, that's fine so far as it goes in being "a best outcome" but if that is true, then logically my example of "a best outcome" for Pietro defending himself of Pietro defiant bravery against overwhelming odds turning the hearts of the bravos in his favor must also be among the "best outcomes".
The authors argument depends on the idea that the fictional position absent any rules to quantify the fictional position is enough to constrain the outcomes of the scene such that only some particular outcomes are possible. And while I'm sympathetic to the value of fictional positioning, I think he's just wrong in that.
To make it seem like his fictional positioning hard constraints the outcomes, he's very selective in what he allows the outcomes to be given a stated fictional positioning.
If you are imagining cases that are so far afield from what Harper is positing, to the point of claiming they are "cheating," then clearly you have different parameters for what the fictional position is establishing here.
No, absolutely I don't. That's my whole point. No matter how rigorously you define the fictional positioning, if you aren't quantifying it in some rules way (which his variation of my "World's Simplest RPG" cannot by definition because it only has the given rules) then you aren't actually constraining the possible outcomes. This is particularly true if we are allowed to in our "a best outcome" and "a worst outcome" stakes introduce new facts to the narrative (as many Nar games would allow), but I would argue that it holds true even in the case that we are not. Again, notice the variation in how Pietro's defiance or meekness are treated. Either that depends on introducing new facts to the narrative (in which case why in one and not the other), or else the author is cherry picking to make his argument seem stronger than it is.
UPDATE: Let me try to clarify what I'm saying in more technical language.
Case #2 and Case #3 of his examples are supposed to be the same example with different undertaken actions. The same fictional positioning is presented in both cases.
In one however the participant with narrative authority decides that the best possible outcome is partial failure, while the worst possible outcome is critical failure. While in the same case for a different action the participant decides that the best possible outcome is partial success and the worst possible outcome is critical failure. Nothing however about the fictional positioning explains why one action automatically constrains a best possible outcome to partial failure and another action constrains a best possible outcome to be partial success.
And if the purpose of the examples is not to show that those constraints can be derived from the fictional positioning, then there is no reason that in any of the three cases one of "a best outcomes" isn't always critical success and one of "a best outcomes" isn't always critical failure. And in that case, fictional positioning doesn't actually matter in the sense that the author is trying to argue.