Riot I'm curious why you are nerfing Sion's E mana

Honestly? Because he was successful in a role.

Edit: because they probably felt his skill shot aoe shout was too 'overbearing' and has 'no counter play' despite sion literally shouting it's counter when he uses it. 'You can't hide behind lackeys!'

Because Sion's E was so great of a laning tool.

Spam it to poke enemies down in lane for large amounts of damage and clear waves nicely with an absolutely nonexistent mana cost. Ranking it up granted you so many benefits for zero increase in mana cost. Reduced cooldown, increased slow, 50+ base damage per rank if you're using it right, waveclear, etc.

Its base damage is very, very high when you use a minion to hit a champion. Its high slow made followup with his Q and ultimate and jungler ganks very easy.

He was just a very good champion top lane that could use his mana very efficiently to win almost any lane matchup and apply pressure to the rest of the map with his ultimate.

Because he was broken in top lane and while it needed to be nerfed, they still need to do something about ranged top laners.