Meanwhile the Spanish and Portuguese are going to be building up their own forces and quietly or not so quietly siding with the British. Spain knows damn well it’s likely to be next on Napoleon’s menu, and Portugal and Britain are allied through the Treaty of Windsor. So now there’s an army that could actually threaten him, and if the British need a base on the Continent, they have it.
Nappy isn’t going to be building ironclads; sure, they may technically be feasible but that assumes he actually knows how they can be put to use and has the engineers to do the hard part. Which he doesn’t, at least on the first part.
Meanwhile the Royal Navy isn’t going to be idle, since they’ll damn well recognize the threat for what it is. They know if the French land they’re likely fucked. So they’ll also be expanding, and they can build better and faster than the French.
Could he defeat the British? In theory, yes, but that requires him to change his behavior and personality, and assumes the British won’t change to meet this new threat. Which is quite frankly absurd.