He is literally a meat shield. Nothing more nothing less. And a squishy, easy kiteable one at that.
Sion is the farthest from being a viable Tank compared to: 
I won't go into detail but if you play a game of Sion you will understand the struggles.
Ecodeath2 votesyeah he is pretty op sporting a 55% winrate and needs a rework to put him in line
KrugLyfe1 votesBuff him a little easy as that. He's already strong just not on the same level as other tanks.
Incognonymous1 votesI think he can be easily fixed with a small base stat buff, the reversion of his shield recast nerf, and a reversion to his size nerf.
Best KhaZix Void1 voteshe's supposed to be easily kiteable, if his kit was easier to use he'd be best tank in the entire game.
A good sion is infinitely more disruptive than any of the tanks you've listed.
Olath Quortek1 votesHe doesn't need another rework. He does exactly what he's designed to do and he does it well. "Meat Shield" is the perfect way to describe a tank. He brings up to 4 seconds of aoe CC with only his Ult and Q. E has a decent aoe slow and Q is on a short enough cooldown to be used multiple times in a fight. His W can deal 14% of each opponents maximum health not to mention base damage. He can be infinitely tanky, scaling extremely well with both Cinderhulk and Titanic Hydra. He brings a pretty close to even split between Physical and Magical damage too. His base damages are actually pretty ridiculous if you can land your abilities and he has all of the tools he needs in his kit to land them. His passive is potentially the best after-death passive in the game. He has massive amounts of zone control.
Honestly I could go on. Is he hard? Sure... Is he bad? Nope! I play the hell out of him and I understand the struggles are worth it.
Good luck to ya! :P
