And I just completed the achievement yesterday. But this is a rare case where I don't actually really mind. The first <100 battles I captured pets I didn't yet have and the rest were spent leveling pets, so I got a lot of pets to lvl 25 while doing the achievement. It was a good reason to grind
500 was probably a bit too much for just getting your pet menagerie upgraded to lvl 3. I think 150 is good because it's closer towards "capture all draenor pets, possibly hunting for a good breed / rare one, and then battle a bit extra" than "you did all that, now go do 400 more battles". 150 is still a lot for people who don't do pet battles that much. They should nerf Draenic Seed Collector
as well, though. It's ridiculous compared to the mine.