The equipped pet buff reward for saving 5 pets doesn’t seem to be doing anything. What is it supposed to be doing? As I interpret it, his affixes should be raising closer to their respective caps, but after getting it twice nothing has changed that I can see.
If you completed that feat, it increases one random affix of the pet you are using (equipped). The increase is not that high so you have to check your pet affixes before and after you complete that feat and see which one got increased. 
I did, I took a screenshot before I got my first one. I know it definitely didn’t change after the first. After 3 or 4 and I look at it again, my 11% MP is now 11.4%. Perhaps it didn’t change though until I logged out or something, which I rarely do. I’ll continue to keep an eye on it though.