I've made significant changes to the study after having tested the first Vular on Numa Prime - Uncharted Ruins. You should really give the study a re-read. It just about proves that the harder the enemy hits, the more increasing armor protects you. It's still probably not enough to make a lot difference, though.

For Guardian, my guess is that increasing a character's armor by about 10 will decrease his damage by 1. So my bet is that a skill like max Protection will decrease his damage by about 6 per hit. Max Increase Mass would decrease his damage by about 30 per hit. The guy probably hits in the 100-175+ range, so whether these skills are worth it is up for debate. I continue to think that Protection and the Dura-Implant are pretty worthless, but Increase Mass does make some sense.