A group of 5 players who are new to the game and without BoA's are not breezing through dungeons healer-less. If there are places where that could happen, then the tuning is definitely wrong, but that's what the leveling experience has to be balanced around, because not everyone is going to be decked out in BoA's and running a dungeon for the 1,000th time.
I definitely agree that the WoW leveling experience does a poor job of preparing or teaching people about max level play, but increasing the necessary coordination and skill required for leveling dungeons is not the answer. That will just lead new players to level without doing dungeons because they'll be too frustrating, or cause them to quit.
What should be done is to utilize proving grounds type solo instances every X number of levels which slowly introduces players to their class abilities and role as they level up. If that sort of system was in place then you could have some more increased responsibility through the later leveling dungeons, but you can't just make those dungeons harder and expect new players to just figure it out.