In Eastern Europe, while they had cannons, muskets were a rare thing and they still relied on cavalry. If you look at the videos, many of Michael the Brave’s victories relied on good maneuvering of cavalry.
These are all changes that can be implemented in the game, it’s up to the devs whether they want to add them or not.
But if but Age of Empire 4 wants to focus on a shorter period of time, Michael the Brave’s campaign probably won’t be added, which is why I made another suggestion with Stephen the Great’s campaign:
His deeds don’t match what Michael the Brave did, managing to unite Wallachia, Moldavia and Transylvania for a short period of time, but he has done a lot: ruler for 47 years, been at war with all his neighbours, helped was helped and fought alongside Vlad the Impaler and out of 46 battles he only had 2 defeats, at the hands of the Ottomans.