@Maxperson has already said he doesn't consider Volos or Mordenkainens as general use rulebooks, as they contain a lot of lore and he doesn't consider monsters as more rules.
Which IMO means he doesn't consider the Monster Manual a rulebook (even though it obviously is), but I digress.
In
@Parmandur 's defense, he has said that if you include a bunch of supplementary RPG content for previous editions, you should also include the DMsGuild for this edition.
My opinion is largely that we are focusing a lot on the count of books, instead of the amount of content in those books, which just seems to grow every year. Last year's adventure, the Frostmaiden, is a whole 320 pages chock full of adventure and content that is well-suited for a frozen environment. It's hard to sell to me that the D&D team is not productive, when they release products like this.
Wildemount: 304 pages
Theros: 256 pages
Frostmaiden: 319 pages
Tasha's: 192 pages
TOTAL: 1,071
If instead, we were given a product with 90 pages every month (which is about the same page lengths) would we complain about productivity?