5-mans should be made into their own form of endgame. They should not be considered "training grounds" for raiding - if anything raiding needs to be de-emphasized, especially in reference to 5-man content.
1-shot abilities are not fun - that was the reasoning behind the stamina increase in TBC and Wrath, to reduce the likelihood of being 1-shot. What we ended up with is health pools that are so big now that they just seem... weird. Oh sure, it's just a number but something is lost between having 4k health and 800k health. Especially with percentage-based self-healing in a game that wants to continue to claim to support PvP/world PvP.