The way I see it, you’re navigating between two extremes: quantity of atomic notes (or evergreen, or whatever) per MOC and quantity of MOCs.
On one extreme, if you have 100 atomic notes MOC, you probably don’t have too many MOCs. But those MOCs will be extremely unwieldy and create too much friction. They will probably also be so general in scope that they won’t encourage closely linked thinking.
On the other extreme, if you only have 3 atomic notes per MOC, you’re going to have such a proliferation of MOCs that you won’t be able to keep track of them all. And you’re defining them so tightly that you’re not encouraging linked thinking.
So you’ve got to find a quantity that works for you, which will vary per person. Probably you’ll find this out just by making more MOCs and seeing which ones you are drawn to the most. I find that 10-15 notes is about my sweet spot. Beyond that, I start looking to split the MOC up.
Another thing that helps me is making lots of super MOCs, indexes of other MOCs. E.g., I have a “Philosophy MOC” which links to various notes on philosophy in general, but also to a “Philosophy Topics MOC,” which links to further MOCs on Ethics, Metaphysics, etc.; and a “Philosophy Traditions MOC,” which is organized by geographical region + era (ancient, medieval, Islamic, Chinese, etc.). My own projects and thoughts can be linked to one or more of these more specific MOCs, and also to a “My Work” MOC.
Another thing to keep in mind is that you won’t remember what all your MOCs are, and you aren’t supposed to. Otherwise why bother to write them down? As long as you can find what you need at a given time, that’s all you need. I have rudimentary MOCs (usually just lists of links or even backlinks) on topics I probably won’t touch for years. That’s okay; I pick at them as I feel inspired and if I ever want to write a paper about them, I know where to look. If not, I had fun along the way.