Thanks for this interesting follow-up.
I have some thoughts on this as well which I'll try to be succinct on:
"RTS is about pushing little groups of soldiers around a board that have essentially no agency of their own. Without direct instruction they remain where you left them, waiting for you to push them around again. Therefore immediately there is a control limit as to how many units you can feasibly manage"
I absolutely agree with you. That's the reason in the article I talked about how important AI is.
For example, this was one of the first design challenges in Ashes of the Singularity. Having 3,800 units running around (for instance) a world is a tech demo unless you have a design that lets you effectively manage them.
So how we do solve that in the real world? We have companies/divisions/armies that are expected to act on their own to a certain degree. In Ashes, there's the Meta unit (the army). You take your unit mix and turn it into an army. It then becomes ONE unit. Because of multi-core, the AI can then look through that army and have it act together intelligently.
Thus, the number of things you need to pay attention to remains the same. However, the depth of it is greatly expanded.
The result of this is that RTS is a very lonely, hyper aggressive, hyper competitive gameplay that develops a very long, complex bell curve with a long, slowly descending tail of skill level. That was its hook back in the day.
Frankly, that could be said of any genre that has an online component.
An RTS game does not need to be MP centric. Ashes, for example, is not. Most of the maps that come with the game were based on the idea that players would be playing against AI opponents.