That's one way to do it... but there's also the fact that DS is on a specific timer, like everything else in the game. It's like ADS' High Voltage, it's always going to come after x seconds but sometimes that gets pushed back by another skill (added by the nodes in t2, added by new phases in t5). Divebombs come roughly every 31s, and to optimally do your role you can plan your rotation around DS and know exactly when you need to hit that IB button. Paladin is afforded the luxury of hearing the sound and hitting the button whenever since all their mitigation is off the GCD. It's not ridiculously harder than PLD or anything, but there's a difference in how we plan our mitigation.