Sion shouldn't be able to time out teams. His hatred shouldn't be able to go off as soon as he revives, that's the most broken thing in the whole game. He shouldn't be able to 1v3 or 1v4 whole teams. ...
Take out Sion before the cooldown. It's really not that difficult. I take down 7*, g12 Sion every day. If you don't want to bother with him early, stun him and leave him until later. Buff block so he can't taunt. Attack smart.