It is actually fine. 10 % would make it worthless.
That's not true at all, damage reduction is a massive buff. Rangers had 10% reduction just on themselves and that was deemed OP.
I don't know how you think that's apples and oranges. It's damage reduction in both cases... Except in p4 case, you have tanks taking an extra shot to kill. Explain how you could possibly view that as worthless