It's been a rough week for me, so I'll just say this - I don't know how you could hate the grummles. Their origin - created by the mogu out of troggs - means that not only are they one of the few intelligent races on Azeroth made both by another race native to the planet but from another intelligent race, but they also illustrate some interesting flaws and aspects to the mogu and their thinking. The mogu, upon discovering the troggs in the mountains of what would become Pandaria, decided to improve them.
What's fascinating is how they chose to improve them. In looking at the grummles, what we are looking at is the perfection of the aspects of the trogg that the mogu saw as worthwhile. So when we see that the grummles can move heavy loads at reasonable speed over long distances, that they have acute senses of smell and unerring senses of direction, we see that these were the aspects of the trogg that the mogu sought to amplify.
Physically, at least, the grummles were a success. Well, one could argue that they failed when it came to being strong in order to crush the mogu's enemies - modern grummles aren't even capable of fighting off the hozen that plague them. It's clear that the grummles possess great endurance and the capacity to carry heavy loads long distances, making them excellent at packing and hauling. They clearly have strong senses of direction, dating back to their original uses in supplying the slaves laboring to erect the Serpent's Spine.