So I'll adress both points at once from those arguing for the current system:
1) The pint of AI not being smart enough to effectively use the system as well as a player is kind of something I addressed. It'll never happen and that detracts from difficulty and the game as a whole majority. The game is built around single player and thus AI plays a big part in that. The system used should be just as beneficial to the AI as the player. Not showing the clear disparity is does. PvP isn't a good argument in this case as it's the AI the player will fight against and there's no way I see the AI ever being as good as a player with things as they are.
2) Not everyone likes mechanics of combat playing out like chess. Also, the idea that chance D20 takes away from determinism is wrong since you have the option to build RNG in your favor or not. While building 90% chance to resist isn't the same as denying the chance for CC completely it's sufficiently powerful enough that your choice matters. Adding elements of surprise retain replay value and the ability to make each turn impactful and pressured since you're never 100% certain. Further, I'm arguing to keep the armor on top of this chance system. Thus your ability to prep plan and gear isn't hindered. Nor am I taking away from your determination to optimize your party a certain way at all. I'm just adding another element of depth on top of it for after the armor is gone.
Edit: Let me be clear, I'm not saying the D20systen was best (CC was god mode after all for much of the game) but I am saying that combining both systems so that you have too layer determinism and bottom layer chance adds much more depth to the game and would improve everything. It's also improve ability options and solve the shield sword debacle in part
Edit2: It also gives more tactical options as you plan both your armors and gear and whether or not that's your only line of defense or your first and how strong that second line is at the cost of other abilities. We also have skills that penetrates types of armor. This would a second layer of tactical thinking in how that works and whether or not we should go for it or if we want to ensure the same cant happen to us. There's also the fact that'd promote use of loremaster as it compels players to check status checks the AI might have beyond the armor we can obviously see.
