My question is my post.
It's certainly not a work of systematic philosopy... calls itself: An Essay on Man in Revolt.
The Plague is, in effect, a narrative of ideas. Does that make The Plague less a work of fiction (many would agree to that), but why is The Rebel. for calling itself an essay, less a work of fiction?
It's as possible to read The Rebel as a kind of fiction... with disguised protagonists, action as ideas (with consequences), as it is to read (dismissively) The Plague as weak philosophizing. In fact--reading The Rebel as a work of fiction... a Fictive Essay, would involve a far richer reading than any I've yet seen.
Hannah Arendt's The Human Condition begs for a similar explication.
So yes, maybe it is the critical apparatus that is the problem.
The critique in each case depends on holding the one and the other to definitions of genre that each clearly refuse to submit to... an evasion of dealing with either for what they are.