Not sure that binary is such a bad thing if you are referring to going from 50% to 100% health in one cast :P

It seems that the 4 ret team sort of works as a mediocre survival sort of squd for 100 seconds then 20 seconds worth of kick ass time every 2 minutes. Considering the sort of sporadic fighting that ossurs in BGs again, this probably isn't a horrible thing. If the team can stay alive in between having cooldowns to use then they can still be a force to reckon with considering BGs is quite often about surviving most rather than killing most.

Saying all of that, I think the durability of having a dedicated healer in a 5 box team can't be understated. They have more effective heals and cleanses so will generally be a better rounded team IMO.