I'm not sure if it's old news or not, but i tested out Protect, Rampart, Defender, and all three together. Either way I still took the same damage.
I'm rank 15 and tested on a mole, I used the same one so as not to skew the results. I let it hit me 10 times, low end dmg was 18, high end was 26 (only happened once, 25 happened a few times).
I know this isnt a very large sample but It's enough for me to take them out of my skill bar.
May test later on harder hitting foe and see if theres a difference but for now i wont be using them