I am very curious to hear your examples of improvements/activities on land that become part of the unimproved value of land at a fast enough rate to matter?
Of course some portion of the taxes go to Disney. Who do you think pays for the air travel system that brings people to Orlando or LA? Who pays for the freeway system that brings in the food?
Re your last argument, the word “mostly” is doing an obscene amount of legwork. Obviously the unimproved land has a market price $X and then the land + structures on it have a different price $Y. So no, obviously the separation is not a fiction, but any particular dollar value is certainly a bit subjective and fuzzy, just like all appraisals are. For what it’s worth, appraising unimproved land is much less subjective than appraising the land + improvements, which we use as a tax basis today.