I think one interesting point about the amount of setting material is how modular Golarion is. Most campaigns, even most APs, can be run worrying about anything beyond the bounds of a single country.
If you're running a game in Ustalav, for example, you'll want the Ustalav book to break down the country and the details in the Ustalav book about it's relation to its neighbors. Maybe if you're feeling really gung-ho, you read up on them on the wiki.
Some areas are more detailed than others, of course. You could get a half-dozen books on Varisia or a couple pages in the world guide on Isger.
So, the number of books you "need" to stay within canon on any individual campaign is generally quite small. In a lot of ways, it's more like having thirty settings with roads instead of, say, Sigil or spelljammers connecting them all.
I think my post spells out a much better process than I follow consistently.
Sorry, I probably should have unpacked that more. I use a very similar process to you, just hadn't really thought about it in stages.
The comparison, though, is to my normal (non-AP) prep time. That tops out at about ten minutes, usually less. So even a very streamlined AP prep bumps over that.
I still think, and my players still think, it gives them better games, though. So there's that
Cheers!
Kinak