If Riot wants new Sion to be tanky...
Why did they remove everything that MADE HIM TANKY? No more DR passive, health gain on kill reduced from 3 to 2, and he loses ~700 base health at level 18, going from the second highest base HP in the game to second or third lowest.
Sion's major weakness was that he was easily kited, but the rework just makes it worse by removing his unconditional hard CC with a charged skillshot and slow.
'We took away Sion's innate tankiness because we want you to build him like a tank, even though his innate tank stats weren't enough to keep him alive long enough for him to be viable to begin with'.