If you do rework Essence Reaver, maybe you could put its effect on Renekton's ultimate.

The fact that Renekton in particular actually makes decent use of Essence Reaver leads me to think that maybe Dominus should just have that effect innately. Maybe without the AS, but just the "basic attacks refund a portion of basic ability cooldowns" part. I don't know about the exact numbers, that's not my department.

It would also make another parallel to Nasus' Fury of the Sands, now that that reduces Siphoning Strike's cooldown.

Also, I'm not sure of its actual strength since I've never really played Renekton, but Dominus just sounds extremely underwhelming on paper. Especially compared to Fury of the Sands after all the changes it's gotten.