Heals were severely nerfed to about 1/3rd of previous values if I recall well. I have tested cleric (aka priest) and decided no matter what I do I can't outheal matron in PvE... mainly because I am human and my reaction time is longer than her
Healing other ppl is tough job now, every single boss has nasty specials and healer has to avoid all of them and keep an eye on pt members at the same time. It is VERY taxing and takes great amount of skill (simplified training grounds for that are BGs).
I have not tested summoner but from my experience I know they can handle healing a lot better than cleric and at last the same as warden.
P.S. If someone in pt/raid dies it is always healer fault... You are going to be insulted a lot before You get skills needed to keep pt/raid alive, be ready for that