Tank mentality.

[Vyserion]

You're assuming they were using Shroud of Saints.

Btw, I was the tank, and I had full DL, Garuda's Gaze, and an optimal rotation, as well as spreading my cooldowns.

Tanking Titan is pants on heads easy, but you're really underestimating just how easy it is for a WHM to overheal in this fight without multiple uses of Shroud of Saints.

This.

When doing Titan for my WHM Relic, even with experienced and well-geared tanks, I had plan out my use of Shroud in order to not take threat. Your first few sets of Medicas during stomps essentially guarantee that you're going to be riding the tank's back with threat. Obviously lesser geared tanks have problems, but I frequently have to shroud either just as I transitioned into phase 2 after a Divine Sealed Medica, or sometime shortly thereafter. For threat, not even for mana issues.

It's easy to out-threat damage dealers. A White Mage can ramp up essentially unavoidable threat simply because he/she is forced to heal everyone. God forbid your first Medica during stomps crit all targets.