But you also have to keep in mind that the rage we gain from damage taken ALONE is not enough to give us a 100% uptime. You also have to consider the amound of rage we generated to the amound of damage we take. The closer the gap between aktiv generated rage (shield slam, revenge, ...) and passiv generated rage (damage taken) is, the stronger we are with IP. When the damage income is so low, that you generate a high amound of your rage aktiv (shield slam, revenge, ...), you have a lot of "extra" rage for IP to absorb the almost non existing incoming damage. When we run into a hard hitting boss, we generate more rage from damage taken. But the overall amound (aktiv+passiv) of rage we generate to the amound of damage we take is lower, because the amound of aktiv generated rage is not as impactful in a high damage situation as it is in a low damage situation. That where IP starts to fall off and % based dr active mitigations will start to shine.
Thats why i made to comparison with the DK, because they are in the same boat with their death strike / blood shield combo. They are almost immortal, when the incoming damage is so low, that the stay in range of their min. death strike heal. But its a other story in high damage content.