High damage pet builds that can clear quickly without any concern for defenses can get away with this. For many pet builds, however, extra armor can be the difference between being able to escape a hit and heal while your pets take aggro and getting 1-shot, especially in higher SR. I wouldn’t take the augment just for the armor increase, but the pet Bleed resistance is huge for non-Shaman pet builds like Cabalist, and the armor is just extra icing on the cake. For my playstyle, the difference between 1400 Armor and 1800 Armor is enormous - you get so much more breathing room in preventing damage spikes any time a nasty mob looks past the pet aggro.
I made a thread specifically on pet augments last year, but that is more aligned toward weapons than jewelry.