It's not that vi and j4 are OP, if you think back before season 5 they were never considered to be op, what makes them seem so strong is the fact everyone else is so weak. Play someone like amumu, naut, eve, kha, rammus and you will realize they can't sustain in the jg. Normally with them you spent a large portion of the early game just trying to farm and backing way to often compared to the likes of the top 4-5 junglers. In the previous season I even saw amumu and rammus bans, it's not like they got game changing nerfs between now and then, it's the fact they can't clear the jungle to effect the early game.
My point is its the way the new jungle is designed that is the cause of this mess.