When our ilvl goes up, our mana pool DOES NOT INCREASE.
Yes, our healing spells heal for more life. HOWEVER, there are lots of situations where there is a ton of damage across the group and it costs a lot of mana. Which also means, that bad a$$ super cool heal i just did, was for that damage and not the next.
Blizzard recently nerfed some of our healing output.
And, with all of this, you want more dps, which takes mana.
You want more dispells, which takes mana.
Just because our heal can add more life this time, does not mean jack when the next damage hits.