It took you 7.5 minutes+ too reach the 300k mark...so you got over 500k in the second round in under 7.5 minutes?
Did you and that healer with 772k healing run to some corner and go back and forth?
You're either the god of operatives, or I need to reroll...because the closest I've ever come to that is a little over 600k, and I had around 18 medals with that damage, which means I was near a door most of, if not the whole match.