While I know it's not a popular suggestion with some members of this community because of how badly the implementation was botched with another well known game, there's always the option of scaling enemy encounter levels to the party's current level.
Speaking of difficulty in other games, I have a lot of fun with the tactical combat in Blackguards because it is (in my opinion) pretty well balanced and challenging (but not impossible). Its design is able to get away with using set encounter levels because it maintains a pretty tight leash on the player's rate of advancement and where they are in the game world.
Divinity does exactly the opposite. You're free to go where you want, mostly whenever you want, and based on how aggressive/psychotic you want to be with your party each player will experience wildly different rates of advancement. Without some sort of dynamic scaling, I feel they developers are facing an impossible task of finding a challenging balance for every possible style of play.
