@Macaras: @Umbra's solution seems preferable to me because it acts directly on the late period without affecting the early period.
Concerning the power of the AI, the amount of money it has, the number of armies it can generate simultaneously, it would be necessary:
1- either put the same financial brakes on him as the player
2- or, in the case of the most powerful factions like HRE or ERE, other limits to prevent it from producing so many armies in a chain... undoubtedly more difficult to implement to find the right balance