Bill Zebub
“It’s probably Matt Mercer’s fault.”
I think the semantic argument has become silly. If I ask you in what book the rules for Beholders are, what will you say?
Mostly the PHB. Actions/reactions/bonus actions. Initiative and turn order. Attack rolls, saving throws, movement, etc. etc. etc. etc.
Where do you find the rules for, say, an ogre?
EDIT: And I'm really not just being semantic/argumentative. I see the MM as in the same category as Adventure Path: primarily content to be used with the rules.