So why does graves need a nerf?

Good damage, decent survivability, god-tier clear, above average mobility, and Smoke Screen is one of the strongest abilities in the game.

He pretty much has everything you could ever ask for in a jungler and you can see that in his win-rates above Gold+. I personally don't have much of a problem fighting him either, but then again, I'm not ranked.

He scales harder than Jax it feels like, and Jax is a Libra

Red buff graves is impossible to get away from (especially with his W slow buff) and he can duel a majority of junglers in the game, due to his free true grit resistances. He can burst a lot of people down while kiting them too, Q into a wall is burst damage and he can get 3 autos early while most champs need attack speed items (and these autos hurt).

There's other strength issues besides dueling too, like his superior jungle clearing, able to outpace majority of junglers in the game, racking up the most farm sometimes on the team and having incredibly strong damage.

When fed, he just blows everything up with ridiculous brute force, and his itemization can either make him unkillable or incredibly bursty

Because he is crazy strong