In the 1-49 bracket? Trauma probe and preventative medicine make that kind of difference? I've hit 170K, almost completely ignored in a WZ, and felt like I never stopped casting except for ammo issues where I feel fairly constrained under pressure.
I just don't get those numbers and wonder if there isn't internet bragging inflation built in, or you premade, or something.
Still level 37. I do have a cybertech and artifice character churning out artifact modifications for every level. Trauma probe makes you immortal when facing bads. I find that I heal better on my commando than my lvl 28 operative but I might need surgical probe to not run out of energy on the operative. Otherwise badly geared people take a lot of burst damage in 10-49 that I feel is easier to heal through with the commando than my operative. It's important to keep energy regen on max at all times though. Don't heal those you can never save either. A waste of resources. Focus on the people that make a difference in the warzone.
And no I don't premade on that character. I think I had a guard on me only once. It's all about LOSing and hiding.
EDIT: So far 300k healing has only been done in full length voidstars when freecasting. Otherwise in normal warzones I average out around 230-250k healing.