There are a lot of errors in these:
1. I said 50% avoidance, not 45%
2. You didn't take critical hit confirmation into account
3. You didn't take Heavy Fortification into account
4. Monsters do x3 critical hits and hit on a 20 only
If we assume no Heavy Fortification:
High AC:
- Normal hit: 9.5*50= 475
- x3 critical hit: 150/2= 75
- Total damage: 550
No AC at all:
- Normal hit: 18*50= 950
- x3 critical hit: 150
- Total damage: 1050
Note: If there is no fortification at all, the numbers are more biased toward the high AC character than what the numbers show because being hit for 150 damage all of a sudden is far more threatening than being continually hit for the same damage. Thus, the low AC character's change of survival is lowered.
If we assume Heavy Fortification (which is more realistic):
High AC:
- Normal hit: 10*50= 500
- Total damage: 500
No AC at all:
- Normal hit: 19*50= 950
- Total damage: 950
However, that's for comparing the damage taken.
If we look at the damage avoided:
- High AC: 10*50= 500
- Low AC: 1*50= 50