Small Sion buff

Sion´s reward for farming and playing exceptionally well is that he gets the same stats as any other tank. If you play average you get punished. It´s a similar story with all his other abilities. Riot could atleast make Sion´s base armor scale a bit more with say +1 per level extra Similarly He could get + 5/10/15 % armor/magic pen on his ult so his damage won't fall off as hard come lategame

Giving him a small buff to his armor scaling would keep him on par with other tanks. He will still need to farm his health.

And unlike other tanks Sion does not really have a more focused source of damage On a Maokai or Malphite you can wriggle in an abyssal sceptre if you want a tad more damage. There is no single damage amp item for Sions abilities. His damage tends to fall off really hard come lategame a small amount of hybrid pen could help him stay relevant. Unlike most other tanks his abilities are incredibly telegraphed 2 second charge Q 3 second charge W globally announced ultimate which isn't the easiest to land from a distance. Meanwhile everyone and their mother can land a malphite combo reliably in less time then sion needs to charge is Q. It also deals good damage and if you want to upgrade your damage simple, buy some magicpen.

TL;DR Sion could use some better scaling to prevent him falling off too hard in the lategame.