Sion Has Way Too Much Counterplay

Seriously, he's so slow, so he's easy to kite, his ult is easily sidestepped, his Q is VERY easily sidestepped, his E is a short range very low damage skillshot that applies a wimpy slow, and his W deals no damage if it's popped. Why does he have SO MUCH COUNTERPLAY. It's not like he has AMAZING tankiness to make this all worth it, he's wimpy as hell. His damage is mediocre and it pretty much ALL comes from his awkward autoattacks since anyone with half a brain can dodge any of his abilities. All of this, gets amplified by a million when the enemy champion has a dash or even just a movespeed steroid, which is... pretty much every melee champion? And then every single ranged champion shouldn't ever even come close to being near Sion because he's so slow and his only way of getting near you is his worthless ultimate that is also sidestepped ridiculously easy? Then there's his passive, it does... nothing. The wimpiest slow in the entire game can stop Sion from doing anything with his passive. The only time it does anything is if your teammates root enemies for you and even then the damage isn't AMAZING. Sometimes playing Sion I literally just go to last hit any minions when I die in lane because I realise that there is no chance I can do anything with it. Kog'Maw's passive is just a better version of Sions as, he has free bonus movespeed for the full duration, his deals more damage than any amount of autoattacks you will get off, and it's aoe. If an enemy team during a teamfight just walks out of Sion's Q, and pops his shield, it was essentially a 4v5 the entire fight. And even if he lands all his abilities perfectly, the amount of impact it has on a fight is extremely unsatisfying. Take a look at Maokai. His Q is an interrupt that's aoe and instant, less of an aoe but it's instant, his W, allows him to become untargetable and root an enemy AND is a gapcloser/escape, his E provides vision, and also slows. Maokai's ultimate does NOT do as much damage as Sions ultimate, but it provides reduced damage for his entire team, and the damage can't be dodged. I don't understand, why pick Sion over Maokai, or really any other tank for that matter.