Honestly, only you can know if it's worth it to you. Do you pet battle at all? If so, Graves is still really strong, even after the nerfs. If not, I would say, do you like the pet's look enough to grind it out? If you're doing it for an achievement, I guess that's really up to you. I personally did it because I collect and battle pets :O
I just checked my stats and it took me 90 wins with the stimpack to get Graves.
Main thing, for me at least, was picking a hero that I liked playing. There's a lot of heroes that I just can't stand to play and made the matches feel terribly long. Find something that works and work on it in bits and pieces.