If the origin of the disagreement is basically labeling, then it's really about the goals of a book called "Monster Manual." That's something that reasonable people can probably disagree about, but I've got a case I'm gonna lay out.
- D&D is a game that one can learn how to play from books.
- The books that teach people to play D&D are the Player's Handbook (which gives you instructions for making and playing your character) and the Dungeon Master's Guide (which gives you instructions for making your world and running the game -- including instructions on how to make a "monster.").
- A third "core" book is released to give the DM additional help in making a game by providing material they can use in their game right away -- it takes the advice in the DMG and shows you how it works in a way that you can use it right away.
- My design meets that goal for the third book better than the classic MM design does.
If we don't call that book "The Monster Manual," (Maybe, I dunno, call it "The Adventure Guide") is that a problem? Lets say 5e was released without a Monster Manual, but with an "Adventure Guide," is that an idea you can get behind?
Because basically the idea behind my format is to make the third "core" book serve the needs that a third core book has.
Yes. As I've been saying throughout, I could get behind that.

Does that necessitate that there be no encyclopedic manual of monsters, stripped out of their individually built/pre-combined habitats? I do not think so.
As I said, it would be a great supplemental. If you want to say "this other work/Adventure Guide" is the more important/better "3rd core book" while I say it is a "really cool supplement that any DM would like to have" then it sounds like we have some agreement. I still need/want a Monster Manual, though.
Now...what monsters go in/lairs get made? How many pages each? How many creatures are balled into each preset environment?
And there's the question of fluff...which many posters here, at least, seem to want as minimized or generalized as possible. Are we going to have a kobold warren of dozens of little dragon-worshippers and half-dragon-kobold sorcerers with a "young" blue dragon at the end...or red...or green dragon? Or a warren of little scaly dog-men? Either presenting with their traps and, seemingly all important vermin. And how are you going to argue/survive the backlash of one preference or the other? Are goblins automatically "wolf/worg-riders"? What about giant bats or giant lizards? Or are we going to have "Forest Goblin", "Subterranean Goblin", "Dessert Goblin" "Tundra Goblin" entries...spread willy nilly throughout the book with fifteen entires in the, extraordinarily important for this work, "Index"?
Are there going to be entries for Goblin Camp, Hobgoblin Camp, Orc Camp, Bugbear Camp...or doing one with some DM's Note that you can swap out the creatures as desired? All of those "cultures" are to be expected, by players, to be one and the same? Or, Orcs and Hobgoblins can be swapped...Bugbears and Ogres can be swapped...and where are the stats for those that don't have their own lairs presented?
How do we defend from the point I've made repeatedly that once you've used one of these little scenarios/environments your players now have a map (mental or literal) of what any encounter with a camp of goblins or orcs is set up like...i.e. using each piece of this adventure guide more than once.
Does the "Crypt of the Undead", filled with skeletons, zombies, and a few wights, include expanded listings for vampires, liches, ghosts, spectres? A human Necromancer or Undeath Domain clerics/cultists? Or will we have "The Cemetery of the [mindless] Undead", "The Vampire's Mansion" and "The Forgotten Tomb of the Lich-King"?
In the "Perils of the Swamplands" lair -which I would presume to be populated by any number of poisonous insects, reptiles and deadly plants and other environmental traps (quicksand/sinking mudholes, flaming gases/boiling pools, etc.)- is the tribal set up of Lizardmen supposed to be swapped/the same as for Bullywugs?...Trolls? or just swamp-living goblins?
Don't even get me started on how/where to build an encounter/lair/adventure that incorporates the width and breadth of Demons or Devils...Elementals...Giants...One entry for Hill Giant Steading, one Frost Giant Glacier, and one Fire Giant Volcano, perhaps? What about the others? Should Treants be listed/treated as "Wood Giants" or have their own place in some "The Ancient Forbidden Forest of the Faeries" setting?
How many places...the "anchor monsters" I think you've called them, are we presenting in this "Adventure Guide"? And how big are we talking? 3 or 5 or 10 pages per "entry"? A simple 150 pages? 200? 400? (at an average 5 pages per entry, with each individual monster's stats, ecologic/interactive fluff, maps, traps, etc. doesn't sound unreasonable, 150 pages gives us 30 "encounter/lair/mini-adventures."
Where's the Rust Monster go? Displacer Beasts? The Mindflayers? The Beholders and Black Puddings? If this is to be the 3rd core book, then the D&D iconic monsters need to be there (at least a good chunk of them)...what's that list look like? Is that doable in 30 entries? 50? 100?
Or are there 15-20 mini adventures of 10-12ish pages each and trying to cram in everything possible (that the designers decide "goes together") into individual "monster den hack-n'-slashes" to cover as many of the bases/basics as they can?
--SD