What it all boils down to is this phrase: Mitigation is subject to diminishing returns, but armour is not
. We use this one sentence to summarise both of the effects explained above. I suppose a more correct sentence might be "Mitigation is subject to diminishing returns, but survivability is not", but most people express it in the first way generally. The distinction between mitigation and armour/time to live/survivability is this:
- Mitigation is a function of your armour and your opponent's level
- Time to live is a function of your mitigation, your hitpoints, and how much damage per second you are taking
These are two different systems that are related. The second one uses the first in its calculation, and works the way it does because mitigation is subject to diminishing returns. Again we stress that this is valid against physical damage only. Once fireballs and shadowbolts begin to fly, it goes to your resistance and hitpoints instead of armour and hitpoints.