By the way, the reason why your experience is like this is because these types of talents are most effective on characters who already have high defense. Basically, defense has increasing returns (i.e. going from 0-10 defense is not nearly as good as going from 140-150). I guess in this sense these are "trap" talents because you could be picking them up sub-optimally.
And anyway, a graze is still way better than a full hit, especially when it comes to something like paralyze or domination.
Why do you say that? The accuracy roll is 1-100, so a +10 defense shifts everything up by 10%. You have to roll 10 less to miss, 10 less to hit, 10 less to crit. Everything on the scale shifts up. I see it as linear benefit, unless your defense is either incredibly low as to always get hit, or incredibly high as to aways miss. Most challenging fights, you'll be somewhere in the middle.
Look at this way. Let's say your defense is such that there is a 50% chance to miss. If you get a +25 defense bonus, you halved the amount of damage/attacks that are going to hit you (50% of the attacks that will hit you versus 25%). By contrast, if you have a defense such that there is a 90% chance to miss, then you only need an additional +5 more defense to halve the amount of damage/attacks that are going to hit you (10% of the attacks that will hit you versus 5%). At 98% chance to miss, you only need +1 more defense, etc.
Just because the numbers in question are purely additive does not mean that the effect is therefore linear. Quite the contrary, in fact.
EDIT: my numbers might look insanely hypothetical, but in Path of the Damned some enemies have huge defenses. Against an enemy with e.g. 120 deflection, getting that deflection debuffed down by the first 20 is more important than the next 20. (Imagine a character with 40 accuracy and examine why). That's not to say that more isn't always better, it's just that non-linear scaling means that each point has a different additive value.
Your numbers aren't wrong, but that's a convoluted way of interpreting them. Yes, at 90% chance to miss, a 5 defense bonus halves your chance to get hit, but that statistic isn't very meaningful. A 5 defense bonus shifts the accuracy rolls up by 5 points, wherever it's added.
If you compare it to damage, an increase of 10 damage per hit to a base of 10 damage is 100% increase, whereas an increase of 10 damage to a base of 20 damage is 50% increase. That doesn't make the 10 damage per hit any less valuable when added to the higher base damage weapon (assuming equal attack speeds), even though judging purely based on percentages would suggest that it's half as valuable. 10 more damage per hit is 10 more damage per hit, wherever it's added.