For example, if a general treats his marshals as drones they will do as drones do. This means if you have them become addicted to General issuing orders every turn, then they will lose themselves when he is not around. General setting goals to his marshals for certain time period is better than holding them by the hand through the entire process. There is no point in marshal being just a messenger, he needs to be independent in giving orders but still follow the goals the general sets.
Biggest issue with this is that there are indeed few good marshals in the game. In my opinion being a good marshal is one of the hardest jobs around, and it takes a lot of time and effort. People probably just think that it's not worth it.
I think it's important to note that while both your first point (treating good people as drones is bad) and your second (there aren't that many good Marshals in the game) are true, we shouldn't mistake the second as being caused by the first. Yes, some people who are good Marshals have been treated poorly by a General who doesn't understand the competence of the people under him and thinks it's his job to pass out orders to everybody every turn. (I was one of those Marshals, in Fontan a couple years ago—though now I'd make a lousy Marshal, as my activity has dropped.)
More often, though, you've really only got one person in a realm who can meet both the strategic and time-related requirements of being an active military leader. That means that every roadblock to getting relevant information to that one person is another step towards defeat—and, more importantly, is one more piece of frustration for that person, with too much frustration leading quickly to burnout.
