Well, I am not in the best position to comment more deeply on those two games, but I don't think the general case is made, at all. Lets think about this:
You and I (A and O) are playing some hypothetical GM-less RPG in which we somehow share authority over constructing the fiction. OK, actually, lets question that formulation, first. Do we have authority over fictional position or not? Maybe there's some other game process which takes care of that. I'm going to choose to explore the former proposition though, with the proviso that I've made a game design choice that could be unworkable. Finally lets honor some form of the Czege Principle (CP) here, as that seems like a pretty accepted concept, in general, again with the proviso that we may need to carefully examine it and see if it perhaps has 'weaker' and 'stronger' forms, etc.
So, A and O somehow produce a fiction, and the characters are somehow placed within it, and some aspect of how that fiction is created, or a third process will then push the characters into action by engaging them in a thematically relevant way (operationalizing the premise). We are both concerned with story, and we are expected to do our part by carrying forward the character interaction with this premise, as appropriate to whichever character we are playing (Ca and Co let us say). Now, I'm going to presume here that Ca and Co interact in some fashion, otherwise there is no ONE story, right? They are both engaged with the same fictional elements and there's probably some direct relationship between them.
Now, your thesis is that I cannot build a system where A can both participate in authoring the fiction in a consensual manner with O, and still be an effective protagonist in the role of Ca. The CP is going to make this an interesting dance, but lets see where we can go with it. I hold that we can accomplish a good design that meets the criteria of Story Now, at least in a real-world sense. I agree with the thought in this thread that pure theorycrafting on this kind of thing is of limited value, so anything we were to come up with would potentially meet with THEORETICAL objections, but its what works in practice that I care about.
I don't know if all this is really something that can even be accomplished in a thread, there are a number of considerations, but maybe a kind of 'map' can be constructed and then used to build less and less abstract examples of play. I really don't see any other way to get past this kind of fundamental disagreement. So, anyway, I would put it to my bosses at work the opposite way "Oh boy! Look, here's a super great opportunity to improve our craft/process!" lol.