I promise you, those 69 geared healers rage quitting are not the good ones. A skilled 69 geared healer with low latency should be able to keep everyone topped off a majority of the time, or close to it. Try mezzing a couple of elites if things are too rough.
A 69 geared healer isn't even going to come close to outhealing the DPS of say the 5 strong droid pack in Athiss that all do Charged Burst for 5K at the same time if the tank didn't use a CD, or the turrets of doom in Mandolorian Raiders. Of course you got to ask why is your tank not using CD, or why is the healer not CCing one of the strong (all healer types can CC any mob not immune to CC)?
Elites generally aren't a big deal. If you want to reduce damage, you should really mez the strongs. It usually makes more sense to mez the elite while your DPS burns down the strongs, but that'd require your DPS know what they're doing too. Nobody is gong to tank 4 strong mobs comfortably in the 55 FPs for a very long time, but at least 2 of those should die in the first 10 seconds if your DPS is any good.