Lower AC is necessary. In turn-based rpg misses aren't funny for most people. It's frustrating when you miss every attack for several turns in a row, but if you lowered AC you have to increase HP or fight will be to easy. You can't just add new enemies because no one wants to wait 10 minutes for next turn. Changes in rules are necessary if Larian wants to sell a game for people unfamiliar with d&d. You can't make game for few thousand people if you create AAA.