I don't recall what rank Brian is atm, but as Napoleon's Chief of Staff, he's intricately tied with Bonaparte's star. Even if he never had another original idea in his life, Brian would probably end up in any position he wants as a reward for assisting Napoleon into the position he's in. OTL, Napoleon "merely" drafted the plan that would end the battle of Saorgio in France's favor and take Piedmont out of the war. In other words, he still had superiors at the time. ITTL, he was the overall commander of that battle. There's also the matter of Napoleon's absolutely fabulous wealth.