I'll bite. What additional 900 pages does Dragonbane need?
If Dragonbane's combat rules are turn based, how does Dragonbane handle a chase scene or other scene that needs more simultaneous action in order to have verisimilitude? Does Dragonbane have a "tackle" type combat trick to throw down someone you are chasing?
Does Dragonbane cover the impact of operating a vehicle or riding a beast? What about vehicles like sailing vessels that require a crew as well as a pilot? Can Dragonbane handle vehicle to vehicle combat?
What about nautical travel rules? For that matter, does Dragonbane handle long distance travel? What about exposure to the elements like heat stroke, frost bite, etc.? What effects to weather have? How does starvation, dehydration, or sleep deprivation impact a character? Do we have rules covering sickness and medical care for the diseased? What are the effects of forced marching or other extraordinary exertion?
Does Dragonbane cover mass combat or being part of mass combat? Does it provide for the DM to have several options such as PC's are participating in the combat as heroes and so can influence the outcome through individual actions? Does it provide for the PC's to participate in combat as commanders and maneuver armies on the battlefield?
What about dynastic play? Does it provide for PC's to create holdings, delegate responsibility to underlings, collect taxes, run businesses and produce heirs? For example, 1e AD&D suggested that you could, but it didn't really provide a framework for handling this from the DMs perspective except fiat and a lot of DM side bookkeeping.
What about underwater combat? What about aerial combat on flying mounts?
What about crafting rules? Lets say I want to make my own magic longsword. How does that happen? Or lets say I want to buy an armoire and a snuff box? Is there a really comprehensive price list out there for bags of coffee or barrels of pine tar or a brick of soap or is the GM just expected to make everything up on the fly?
And does the rules really cover how the world works, not merely for the sake of covering how the world works but for firing the imagination and telling the GM what could be out there. Like, what's the effect of a sacred site of different power levels on magical use? The rules can be silent on stuff like that but then you are leaving it up to the individual GM to have the imagination to imagine a whole world on their own.
I see a lot of OSR type rule sets that port over BECMI or AD&D concepts about these things without realizing just how bare bones and unworkable those are for a GM in actual play. BECMI or AD&D suggested these things existed and were part of the campaign world without actually having playable rules for handling combat between an oared rowship with 300 rowers and 30 marines and another such ship. And I see a lot of people going, "Well, just handle it all by fiat and cinematically, you don't really need rules for any of this. Just let the GM decide what would be the most fun?" But, while you could, there are real limits to that. And you can see this from adventures back in the original "old school" era where instead of having rules in the rule book, every single adventure had multiple encounters where there was a hand crafted minigame trying to handle all the stuff that wasn't in the rules that the GM was supposed to rules bash out in play or at design time.