The game will become several times longer. Battles with neutral creatures will be reduced to exploiting a few "foolproof" methods of overwhelming the enemy with superior forces and standard safeguards against surprises from intelligent neutral creatures. The value of a single turn will sharply decrease (since the player already has a significant advantage). No one will be interested in such "tactics," repeated countless times; in practice, everyone will use the auto-battle feature (and the more intelligent the neutrals, the more often they will use it), as it also saves time.
This type of gameplay (if someone enjoys it) can already be achieved by simply agreeing to play with mandatory auto-battles.
AI upgrades are usually done to make the computer a more interesting opponent, not to change the game's profile. To achieve this, it is not necessary to change the algorithms of neutral creatures, but rather to train the computer to deal with them as effectively as a human player, using feints, removing guards, employing advanced strategies for capturing dungeons, and so on. And it should not be afraid to attack, and somehow build/buy/upgrade/combine troops more intelligently. If it is not possible to teach it chains of actions and strategies, then at least it can be taught to select targets on the map based on the build order, rather than grabbing everything that is poorly defended; this can be taught.