Well 6 people arent mt healing usually. In guild groups we'd have group assignments and mt assignments and ot assignments etc but healing nowadays isn't how it used to be. Remember, nowadays smart healing is what dominates - meaning spells know who to target before the player does. When you pop a healing stream totem or a coh, it automatically goes to the player who needs it the most.
So, for example, on gary when people are getting beaten down for being MCed, the aoe heals that are going off anyway instantly pick that person up even before someone has the need to target them. Now, with a good group you probably have 2-3 people who manually target them anyway to make sure they top off, but in general there's sort of a built in safety. Of course, you can't preheal a big burst like getting hit by purple smash, but in general I do wayyyyy less single target healing than I used to in prior years. That's why addons like grid were so important back then, having to click around raid members quickly.