How to defense equate to HP and damage dealt?

Wow lots of information there, definitely helpful, so thank you! Obviously there was the caveat that your example with Fives is pre-buff to defense. I was really hoping that armor rating/defense/damage-reduction had simply been reduced to a single stat, but it sounds like that's still not the case.

I've actually had some pretty good success running critical avoidance mods (primary slot) for my tanks with some success, as opposed to any health or defense bonuses.