Warlander

This achievement is a grind and a half simply because the basic healing ability you start with only heals 100HP per charge (Has 3 charges) and people wont always be missing HP in multiples of 100. Meaning at minimum this will require you healing people 1,000 times or many more.

So this is my ability setup (and you can do this yourself as well with an untitled cleric assuming you sacrifice some hp/armor.

Class: Cleric
Weapon/Skills 1:
Weapon of your choice
Shield of your choice
Skill 1: Area Heal
Skill 2: Accelerator

You won't have the Area heal ability unlocked immediately and will have to rely on chance to obtain it after your matches, but it spawns an AoE of healing on the ground healing on base level 13HP per second to anyone within the healing radius. Accelerate is good simply because it allows you to get to combat quicker and allows you to escape easier.

Weapons/Skills 2
Weapon of your choice
Skill 1: Heal
Skill 2: Wall

This setup works for me and is where I spend most of my time outside of occasionally switching to melee if any enemy comes too close or because my area heal is off of cooldown. The wall is useful incase someone dies, you can wall off where the enemy came from if it was ranged attacks and revive them.

So the way I played was using my accelerate to get to combat/behind my allies quicker and easier if theyre pushed up. I would always go to where the majority of my allies were in combat and I would cast area heal where I thought would have the chance of gaining the most heals. So objectives. Then I would switch to my ranged mode and focus on individual healing and shooting people down with the automatic crossbow. As well as getting revives on people using my wall for cover. When people are revived they also only spawn with half HP allowing you to get some heals in.

Extra things that help are revive efficiency talents.