We have two extremes: true randomness and total predictability. If we have lets say 50% to hit and dealing 1-2 damage and the target has 4 HP, we will need about 5 attacks (ranging from 2 to lets say 30) to kill the target. Based on this, we are able to design totally predictable system, when you hit everytime, dealing 1 damage while your target has 5 HP. What system will be more fun? If neither, then pseudo-randomness is solid compromise.
That system breaks when you start to introduce additional effects to damage. Like stuns and other non damaging conditions. And 5e rules are filled with these. When i played DoS2 a lot of fights were over the moment initiative was shown. Enemies just never got their turn. Doesn't metter that they had a ton of HP. They just were perma-stuned.
