While I don't exactly disagree with your opinion of wanting tanks to be tankier, it would require a complete overhaul of how raid bosses work.
How every raid encounter works right now: It's on a scripted timer with a hard hitting attack every X seconds. The bosses auto attacks outside of these scripted tank busters are pathetic.
So yes: You are a bad tank in the current meta if after you realize when these sequences come, you then still refuse to go to your offensive stance. You only hinder your team because you won't require much extra healing, if any extra healing at all, and the encounter will be prolonged which can make or break an enrage kill. (In many cases it's possible to eat the tank buster in your offensive stance with just heavy CD's.)
A possible way to shape future encounters would be to increase auto attack damage potency and frequency, similar to the bennus in low-gear level from T12.
I wouldn't mind getting absolutely destroyed from even basic autos.
Personally stance dancing is fun and so is mitigation. Good tanks & healers do both.