Healer's class are always fun to play in my opinion. You have already included the healing concept in your game. But it's interest disappears rapidly though the game.
So here's some possible healer heroes
Requirements : 10 points of rebirth
First skill : That skill would be the skill allowing healers to kill some creep more easily. Every 3-5 (or up to 10) seconds, the hero sends rays to nearby creeps draining from them 0.5*int or 1* int (or even stronger though it would have to be balanced at some point)
Second skill: If it's possible to make it, I would have a skill that would heal 6*int on friendly units (IF the Summoner rebuild has been considered then this skill should work on summons too) or deal 4* int too enemy unit. Cooldown not too high not too slow (around 10-15 seconds) Maybe not self allowed.
Third skill: Either an invulnerable spell too make first skill (because it would still be active) or wave spell (like a shock wave) that heals every friendly unit (self include) by 3*int or damage non-friendly by 3*int too. Cooldown 10 secs.
Fourth skill: Passiv: Each spells got a chance (15% or more too multicast (2 times)) Example: First skill would have 10% chance to send 6 rays to nearby units (rays do not cumulate on same unit)
I think at ten rebirth points you don't have your arma so high on dmg, so those healing spell/dmg spell are strong enough to allow you farm creep in more higher lvl areas.
FEEL FREE TO COMMENT' ADD THINGS, MAKE SUGGESTIONS ^^.