The level 58 pet is pretty good, and not that difficult to control if you park it.
I do think some of the lower level pets aren't great. If I remember right the level 39 pet in particular was quite underwhelming.
The 39 max pet can dual wield with weapons. It’s nice to have but it wasn’t until the 52 pet that I really started to notice the difference. It’s an 8 level jump from the 49 pet and innate dual wield is nice too.