Possibly. Although in the cases of the 81 and 83 Basic sets the designers knew that there was an Expert set coming to expand the roster. That being the case, they would* have cut down on the number of high-level monsters in the Basic set to those they felt they just couldn't live without.Though as all of these were in the original boxed set and '77 Basic, but not included in '81 or '83 Basic , that still suggests the designers saw them as less essential.
With the exception of horses, Monsters & Treasure just has broad guidelines for "insects or small animals" and "large insects or animals", leaving the details to the referee. 1e, as you note, changed that significantly.There were no animals (as monsters) in 0D&D? I pretty sure there would have been some in expert. Lots in the first MM.
If I include the '81 and '83 Expert Rules ('77 was standalone and had no Expert counterpart), that adds 10 more:
- Basilisk
- Fire giant
- Hill giant
- Hydra
- Manticore
- Mummy
- Purple worm
- Troll
- Vampire
- Wraith
Though as all of these were in the original boxed set and '77 Basic, but not included in '81 or '83 Basic , that still suggests the designers saw them as less essential.
Which is a bit funny considering even Tolkein had a Green Dragon.Ah, that gives more context to Medusa in the first list, she sits along the classical monsters here (Hydra, Basilisk, Manticore), plus we get the addition of Giants and more undead 'movie monsters' and a worm!
Still no Green dragon
You've got dragons (because it's the brand), humanoids to fight, iconic low level horror monsters, a mythological monster, a dungeon slime and a vaguely medieval monster to stick on Gothic buildings.
- Red dragon
- White dragon
- Gargoyle
- Gnoll
- Goblin
- Hobgoblin
- Kobold
- Medusa
- Ochre jelly
- Ogre
- Orc
- Skeleton
- Werewolf
- Zombie
So the question is, why? What makes these 15 monsters essential, and not others?
The creators of D&D grew up watching the Blob and similar films that are no longer a big part of pop culture consciousness.The only thing on that list that surprises me is the ochre jelly. While ooze concepts have existed in literature before I would argue they aren't a staple fantasy monster by the time dnd came out. Dnd pushed the ooze to a more forefront position.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.