Parry...

[Zourin]

However! I must submit to you that we have tools for those situations, and they are ALWAYS attacks that the fight is based around. Which means they are beyond predictable. Turn 6's attacks hit for a max of 3K damage, and they hit on a timer, which the healers will always be ready for unless it's the first time they encountered it. Realistically speaking, you can't heal Titan HM, or EXM properly the first time you ever go in, because it's a pattern fight, and until you know the pattern, only luck will guide you through safely.

What you have described is "damage per second", really, and yes, it's handled by experienced healers in a choreographed fight, not the tank (aside from popping cooldowns, so at a minimum it's a cooperative effort). Rotational burst damage is just spiky dps in the long haul. Dodge/Parry/Block is the chance that the healer gets a momentary reprieve to tend to other party members unless they're precasting (risky if the heal is a fraction early)

That said, the OP isn't terribly far off the mark. Increases in Parry offer minimal differences in tanking ability to the magnitude of percents of percents, so there is very, very little difference between most gears within the same tier (other than crafted, which bears a marked lack of Parry). i90 gear vs i80 gear, there won't be a measurable difference in parry rate so much as a difference in max HP and general armor mitigation which will play a more vital role. SE's 'standardization' of stats generally means that even if you stack parry as high as it goes, you aren't irreplaceable by another tank.