Yes, this. Well, maybe not all, it is fine for monsters that tend to appear in large groups to be pretty simple, but more 'elite' monsters definitely.Each monster should have 2 to 4 additional special abilities over what they already have, especially ones that occasionally make use of their Bonus action and Reaction.
A monster whose entire Action section is just a melee weapon/natural weapon and perhaps a ranged weapon needs to have more things to do. A 3rd level Battlemaster has an entire platter of maneuvers they have access to... monsters should at minimum have a couple of those in their tool kit as well.
Matt Colville's 'Action-Oriented Monsters' does a lot of what I think would help out. Only problem is he hasn't re-written the Monster Manual adding his design views to all the creatures yet.Yes, this. Well, maybe not all, it is fine for monsters that tend to appear in large groups to be pretty simple, but more 'elite' monsters definitely.
I think this is one of the things I feel 4e did better. Steal some of that stuff.

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