Sion shouldn't be able to out trade the whole top lane roster
while building 
as his first item. Banner gives no real combat stats besides small amounts of armor and MR, and doesnt even give CDR until its completion. Meanwhile Sion can somehow manage to first build this item in almost all of his matchups even in challenger level play, and he out trades champs who are building combat items. It takes bruisers 1+ completed items to out trade a Sion in lane, tanks can never fight him and he can out wave clear every skirmisher
Riot you could look into increasing Sion's mana costs on his abilities, since with 
and manaflow band he can sit in lane and never go OOM since his Q only costs 45 mana and his E is 35-55 mana, and Sions max E first, even after the changes.
