If I were taking that job, I would wonder about my Boss's stability. It might seem motivating, but heck, the war just got started. Personally, I'd save that message for if things are going south, and the player is loosing VP. When I could see sending it, which would be somewhat difficult to determine is the following. I am still trying to find the right balance for the delay against the AI. And, frequently, I am just not ready for when it ends, and things can get really, really tight for the first several months. Sometimes, I have to pull back from a city, or let it get surrounded, and try to deal with it later. This is when a message like that could serve as a motivation to turn things around.
As a side note on firing generals, there is a great book by Thomas E Ricks, The Generals. He points out that during WW2, the US Army frequently fired generals for not performing. And usually rather quickly. But, they almost always gave them another chance, and frequently they learned from their previous failure and succeeded. But, he chronicles how this practice declined, and they just waited out bad generaling, and bad leadership at most levels. Specifically, the experiences during Vietnam and Iraq. It is a pretty good read.