In 220 gear, in world PvP, with Seraphim, Avenging Wrath, <20% HP, and a critical hit I can hit 40K WoGs.
In battlegrounds, that 40K is actually:
8000 * 2 * 1.7 * 1.2 * 1.08 * .8 = 28,200.96.
This does not include Arenas or MS, which MS can reduce this total down to 21150.75.
At ZERO % HP, with everything AND a critical hit the most it can heal is 75% of my HP. You’re just plain wrong in your claim.