Tell that to monk Solo Silencing turn 2. And just gear? Try that on ifrit EX. Slack of and people DIE. And although Damage output of a WHM is kinda high. DPS are still better in this. And rotations are also a given on a tank and I see those fail often as well.
Timing is everything, on dodging, using attacks, or cooldowns. Be it DPS, Heals or Tank. Everyone has a job to do. And it becomes impossible or neigh impossible of people stop doing it. Period.