I'm going to venture to disagree.
Please do...
I think your theory enshrines a single principle -- justice -- beyond the importance it's given.
Probably, but if my theory is mistaken then hopefully it will be mistaken in an useful way -- that is to say, in such a way that revealing
why it is mistaken will lead to a deeper understanding.
Certainly a "just" story is often satisfying, assuming that we care in the first place. If we had no feeling for the characters in the first place, we wouldn't care who got what they deserved and who didn't. Honestly, from an objective stand point, Westley didn't deserve to win -- he was a notorious and murderous pirate.
So for starters, I think the "deserving" part of your theory is off. It's not true justice, it's who we feel for. I've often found myself routing for clear villains, simply because I liked them more.
Actually we don't know if we was in fact murderous or if it wasn't all just clever marketing (so to speak). Indeed, the only person who he actually kills on screen is Vizini, and he only does that because Vizini has a knife to Buttercup's throat. Compare this to Prince Humperdinck (who brutally tortured Westley to 'death' only hours before) -- rather than kill him Westley tricks him into being tied up.
But your larger point is well taken. You may be right in saying that the justice at issue is not "true justice" (i.e. 'objective' justice, if such a thing exists). However the kind of justice at issue may indeed be
subjective justice, wherein we feel that certain characters deserve to win precisely because we like them. Of course, the connection between our liking a character and our feeling that they deserve victory may be spurious: which is to say, the fact that we like a particular character and the fact that we feel they deserve to win may both be the result of a third fact -- i.e. that they have certain traits we admire (which are more commonly known as
virtues). If you think back to villains that you have liked more than the respective heroes of the story, ask yourself
why you liked the villain more than the hero. Many villains have numerous virtues (they wouldn't be a credible threat otherwise), such as being proactive, goal-oriented, clever, and so on. They may in fact deserve to win because of those virtues, especially if the hero lacks virtues; for instance, if the 'hero' is an annoying, whiny, self-righteous, hypocritical twit.
secondly, I don't think that justice is the only principle which can satisfy. Certainly mercy is just as well. The Power and the Glory is immensely satisfying to me -- the protagonist is the best person around, but even he will confess that he is hardly deserving of hero status: he's a Catholic priest who drinks far too much and has fathered at least one child since taking his vows. Yet, when he shows mercy, returning to give last rites to a murderer, insuring in the process that he'll be caught and there will be no one left to minister to the believers in his area, we are incredibly pleased with his character and how he's grown. I guess you could call it justice that he's caught and executed, but that is hardly what satisfies.
I haven't read The Power and the Glory, so I cannot comment.
And certainly love is another. There's an entire genre of books that don't concern themselves with deserving other than in an oblique sense. Just fantasy fulfillment. (OK, not all romance novels fit that description, but many of them do -- they rely on reader identification with a character rather than what the character has "earned.")
Well there are genres that my theory does not necessarily apply to, such as comedy and erotica. However I do think it applies to Romance fiction (insofar as Romance fiction is more than simply erotica). For example, look at Pride and Prejudice. The novel is primarily taken up with demonstrating how Elizabeth and Darcy deserve one another, in that they both muster the strength and integrity of character (i.e. are virtuous) to overcome their personal failings (his pride and her prejudice). Indeed, in the end all the marriages that occur in the book are just, in that each couple deserves each other: Elizabeth and Darcy deserve each other, Wickham and Lydia deserve each other (in a bad way), Jane and Bingley deserve each other (in a good way), even Charlotte Lucas and Mr Collins deserve each other.