I think it's not so much that HPMoR!Harry claims exclusive agency, as that the plot has railroaded him away from any of the setting's other agent-y characters (or, at least, agent-y characters with compatible-enough-to-engage-in-trade utility functions; HPMoR!Quirrelmort is more of an agent-y Other-Optimizer.)
HPMoR!Lucius Malfoy is pretty agent-y, for example, but Harry doesn't get to talk to him much. When he did in the last chapter, the results were exactly what you'd expect from rationalists collaborating -- a sudden acceleration in both parties' world-taking-over plans.
(Though, obviously, "taking the world on your shoulders because you think you can't rely on your friends" is also a standard bildungsroman protagonist trope.)
That kind of notation is often used while discussing various fan fictions to avoid confusion when people are talking about 'canon' version of character and 'modified'. So it's common to just always prepend which version you're talking about, so HPMOR!Harry/canon!Harry/other-fan-fic!Voldemort etc. etc.
HPMoR!Lucius Malfoy is pretty agent-y, for example, but Harry doesn't get to talk to him much. When he did in the last chapter, the results were exactly what you'd expect from rationalists collaborating -- a sudden acceleration in both parties' world-taking-over plans.
(Though, obviously, "taking the world on your shoulders because you think you can't rely on your friends" is also a standard bildungsroman protagonist trope.)