So I recently picked up ICRPG (Index Card RPG) a RPG book by Runehammer (previously known as Drunkens and Dragons)
It’s currently on it’s 2nd edition, which is an A5 book with about 200 pages with text slightly bigger than DnD writing (or very close).
DnD has a variety of books; Core Rulebooks, Monster Manuals, Campaigns and advanced characters all over it’s 40+ years lifespan (first published 1974).
In ICRPG Core Rules, there are 2 Campaign Settings (Dark Fantasy and Space), 20 Classes and 10 Races (over 2 Campaigns), 29 Monsters and a series of adventure hooks.
Yet I feel, as a GM, I can get more out of this than DnD.