I, for example, am ranked multiple times despite being very defence-centric and I never scumbag. Ever. I don't even /sit. I'm pretty good is what I'm trying to say. Yet, my Tortos parses all look dreadful because of the way my guild did it - namely, I took the bats but we stop killing them after two thirds of the fight while I just kite them around.
Again, I know you're not saying "good tanks do good damage rofl", I just want to make it clear that you cannot always apply that rationale.