Good golly why do people do this, it's always a terrible idea. It was stupid when the FATE people released 200+ behemoths and it's stupid now. You are releasing a rules light system, being less than 20 pages long is your selling point. For the love of Madokami this isn't that complex people.
450 pages does sound like a lot, so I just checked my PDF to get the breakdown.
The book itself is 110 pages, but the
character sheets and rules without the explanations are 37 pages total, and completely free. so long as your GM has an understanding of the rules everything you need to play is on those 37 pages.
Pages 1-83 are the introduction and explanation about the basic rules and how the game plays. It gives the rules, which are generally a 50-60 words long for the rule, and then an explanation of how to implement it, including examples of play so you can read the move in action. The book isn't just written as though you were new to powered by the apocalypse, but as though you were new to RPGs in general.
Pages 84-157 are descriptions and rules explanations for the 8 base classes. The only time I've needed to refer back to these is when answering questions about specific rules in a forum, usually when someone asks about Druid's shapeshifting. The information needed to play is listed on the 2 page character sheets and the 2 page basic moves sheets.
158-187 gives all the rules and explanations for the GM to start playing the first session.
188-221 is rules and explanations for campaign play and discussing making evolving, active dangers in your world.
222-324 is all monsters separated into categories of types of environments you find them. I've used monsters from the book a few times, but mostly I make up monsters on the spot.
325-345 is equipment and items, I've looked stuff up in this section a few times during a game.
346-363 is advanced Delving - advice on hacking the game and creating your own rules and content. I've referenced this a few times when writing my own stuff.
364-380 is Thanks section. Personal thanks and then all the backer names - instant NPC name list that I reference pretty regularly.
381-384 is advice on how to teach the game to others. I've read this through once or twice before starting a game with new players.
385-392 is advice on converting modules and adventures from other games to DW. I've read it, but never used it, though I assume this is something that others would find very useful.
393-399 is reference info for tags and creating knacks and drives for NPCs. I usually have separate sheets with this info on the for easy reference, very handy for a GM!
400-406 Index. The PDF ends at 410 pages, with some art and blank pages at the end.
A player doesn't really need to read any of the book since everything they need to play is on a double-sided sheet of basic rules, their double-sided character sheet which also contains the rules for their character, and a double sided sheet of spell if they're playing a wizard or cleric.
The GM needs to read at least to 187 and familiarize themselves with the monsters section before they start playing, and can read more later. That way they can answer any weird "What if X" questions the players might have about the rules. The spacing is quite generous and there's a fair bit of art, so the size of the book didn't feel too onerous as I read it, and I'm super lazy.
Interestingly, the writer of Dungeon Planet, Johnstone Metzger wanted a GM companion that didn't have a lot of the main book in it, and since the whole book is CC licensed, he cut the material up and released Truncheon World which is just the GM parts for easy reference so he didn't have to cart the while book around.
Transforming the field is a very hyperbolic statement, and I doubt the creators or even most of the fans would claim that it is. DW works the way I want to play and GM, I'll leave anything beyond that up to the discussion of others.