An overarching principle goes something like this
Authored fiction counts iff the author is doing so in the agreed way at the right time.
Posters evidently have different ideas of "
the agreed way". For example, one way I've been mulling to picture how many people play knowledge skills is that "
enquiries invite GM to author fiction that is responsive". Where "
responsive" includes - within the notional scope of the player's chosen knowledge domain and responsive to (constrained by) the questions they've asked.
Anyway, reading the debate on features like Ship's Passage and Criminal Contact, to my observation the background principles that determine how those should go, vary group to group. One mode is that one player has authorial control of the setting and other players must conform their fiction to the context they supply (including context supplied ad lib). An example of something similar is where a group of GMs running a shared campaign nominate one of their number to own the setting, or own an aspect of the setting, agreeing that the rest will conform with what they establish in that regard.
Another mode is where authors or designers external to the group altogether have authorial control of the setting and players (GM included) must (choose to) conform their fiction to that context. I think that is what folk generally imply by "genre". A group will follow some norms for what utterances are accepted, and where those norms can readily be seen to derive from an external reference then it's likely those norms are bundled up as a "genre". That's in contrast to the case where the group synthesize messily to produce their genre through play. It's not all or nothing. Choosing to play a character doomed to bring the apocalypse would be adhering to genre when playing Apocalypse Keys, even if authorship of other facets of the fiction were shared. Thus implying narrow and broad, homogenous and heterogenous notions of "genre".
So then the more specific principle you might be interested in goes something like this
Agreement on what fiction should count is grounded in norms.
In that light, if I read your question correctly it asks - who owns genre? Who owns which constraining norms for our fiction? The answer to that evidently varies and it seems hard to me to conjure more than aesthetic or preferences arguments for one or t'other. True genre-less free-for-alls are rare if not absent altogether, to my observation.