E max has been lane Sion's breed and butter ever since his rework.
Sure, you could (and still can) cheese it by going lethality and maxing Q, but that's basically a noob stomp method which makes him all or nothing beyond belief in team fights. His intentional gameplay pattern, since his rework, has always been to max E to poke, and then follow up with a Q > W to trade.
As has been stated, Sion is currently broken in top because his E is bugged and thereby EXTREMELY easy to hit. It used to be one of the narrow's skillshots in the game, but it's currently about as fat as Alistar.