These two have been the top winrate junglers for at least five patches in a row. They provide much more to their team than just Graves does; Ivern in particular, who has a Support's kit with the gold and levels of a solo laner can feel incredibly overbearing. He denies your ADC vision, he denies your skillshots to reach because Daisy, he denies you damage with a shield.
Honestly, I think the jungle has much worse than Graves. Seeing the enemy pick Graves or Lee Sin is almost a blessing, because those two aren't half as frustrating as wasting damage/CDs on Shaco clone or Daisy, or any of the other bullshit those two bring to the table.
To say nothing of Ivern giving all his laners buffs for free because why the hell not