Kind of falling off after what they did to Cho'Gath where he has infinite stacking, since he can stack off epic monsters, champs and up to 6 minions/camps.

However, sion still has a lot of pressure late. With Soul Furnace that does % health damage, and gives permanent health, Decimating Smash that either slows or airbornes, Roar of the Slayer, another slow + range and can displace certain minions like Heimerdinger's turrets and his ult, Unstoppable Onslaught, sion has all the CC, tankiness and damage to provide for a team. If paired with other hard CCs (such as Light Binding etc), you could potentially stun lock an entire team.

His passive is another thing that many, many people either forget about, don't know about or overlook, netting you free kills. After buying Frozen Mallet and Titanic Hydra, theu cant even come close to you without risking dying.