No, it's just Zero's fault for not preparing a proper chain of command and let the others know his plans.
So far they only followed his plan mindlessly. And thanks to Geass Hack they always worked. Zero's followers just believed in his magic without understanding it and Zero was ok with it. They were just mere tools after all.
But the moment he leaves them they become useless because he didn't prepare for that.
Britannia fought with real strategies and good officers they were meant to win easily if it wasn't for that plot-device that is Geass (well duh... it's Code Geass)