Honestly, this line of discussion has me thinking back to my Everquest days, and how encounters were actually far less predictable back then. Especially since you could never fully account for the battlefield itself due to wanderers, patrols, and glitched walls that let mobs aggro through them. Healing classes, especially Druid and Shaman since they had additional roles, had to hold onto their mana for dear life because you never knew when the tank was going to end up needing a top off. Damage also occurred much less consistently throughout fights, and in the worst cases multiple large hits could all happen at once.

I think the difference now is that many encounters are far more consistent, mostly auto-attack damage at low amounts until a skill/spell is used, then the damage becomes much higher over a short period in which our current heals are more than enough to fend off without any worry nor sacrifice of DPS.