Personally, I think Sion needs a fundamental upgrade rather than just higher dmg numbers but with grand mustard preaky boy in charge of balance that is unlikely to pass. Realistically, here's what is possible and still help;
Roar of the Slayer [E] ; I keep seeing demands for 'GROUNDED' effect or just jack up the dmg, both which will never happen even if preak were gone. Instead, how about scaling armor shred based on skill lvl [20%/22.5%/25%/27.5%/30%] ? Jarvan is more or less Sion's foil and his Dragon Strike [Q] has scaling armor shred. In addition Dragon Strike does vastly higher dmg, is much faster and has longer range than minion-less Roar of the Slayer. Even with the minion, Dragon Strike if used with Jarvan's flag doesn't fall short by very much compared to Roar. Also, reducing the cooldown by 1 or maybe even 2 seconds at all lvls would really help. Sion's CDs are all very high but IMO Roar of the Slayer [E] having lower CD would benefit him the most.
Soul Furnace [W] ; I've thought about it and have come to realize that the only way Sion is properly buffed, especially during preak's regime, will be to bite the bullet and lose the HP stacking passive, in part at least. HP stacking reduced from 4 & 15 down to 2 & 10. THIS IS THE ONLY WAY RITO WILL SERIOUSLY CONSIDER BUFFING SION. TRUST ME ON THIS. Anyway, lifesteal & vamp effects diminished or completely null when hitting Sion during Soul Furnace [Shield]. Out of all the shields & champions in the game, Sion+Soul Furnace would make sense as being 'unique' in that regard; IVERN has Sion's shield but able to cast on others+built-in slow+auto-refresh mechanic. Tahm has a much more durable shield & Mord's shield is far more practical & effective than what Sion has. Making Sion's self-shield resist or outright block 'drains' would actually be a helpful buff, would be fully in-line with Sion's lore & wouldn't take up a lot of power budget.
Being truly realistic, Sion is not going to get buffs. Not with ol' preaky boy in charge of balance. Nerfs are more likely to happen than buffs and if 'buffs' do occur, it will be some asinine crap like 'AD growth increased by 0.3 but starting AD reduced by 10'. As long as preakster has absolute power, Sion is boned but if preak is gone or at least not fully in control, that is the kind of buffs I would propose & hope to see.
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