Have you ever tanked all the nim bosses with that gear, with 250 Absorption rating?!
You can get away with much in hm raids, but you wanna tell us that the only way for vanguards is to stack hp?! Hit points are giving you nothing to reduce incoming damage! You are like a dps with a lot of health basically.
This. My PT in 69/72s is sitting at 19.5/40/34 with ~37k HP stimmed. I've also tanked all the new content in HM without issue. Now if I had 78s like you and went for mitigation instead of a fat health pool, I'd be tanking NiM anything and knocking it out of the park.
I have a guild friend that has his tank geared like yours, he's at ~46k, and when we are in parsec together I *always* take at least 10-20% less damage overall than him.