Things they have to improve in next dlcs are obviously theocracies and holy orders, pagans of course but also some balance issue. Id like them to revamp the mongol invasions, the 120k doomstack with no attrition army is not realistic , only way to counter it is to drag them on a coast and throw a doomstack of your own troops stored in boats to prevent attrition. That makes really no sense, russians , ukranians and co are doomed to die if they dont expand to a megablob, theres no option to vassalize and free yourself later , to pay tribute or bribe them to look elsewhere, they really need lot of work, same for aztecs.Also muslims are overpowered, try the fatimid , they roll over anything and its possible to conquer the whole map in a century.
Naval warfare: it needs to be revamped, right now its just useless micromanagement to load in and out troops, it adds nothing to the game, they may as well auto embark and charge you some fee, i know it was not the best era but still theres ship to ship combat since antiquity.