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Orianna's defensive skill is an HP shield capable of reducing damage by 100% and usually over 50% in a lot of trades, and it stays very relivant early and deals with true-damage like Ignite.
Galio's Bulwark in an armor/MR steroid that can only block damage by at most 47%, and significantly less at rank 1.
Orianna's speed-boost can easily be cast on allies or herself without interupting her movement.
Galio's speed-boost forces Galio to stop moving, and it's fairly unreliable to use on allies while also telegraphing their movement.
Orianna's ult applies max CC duration instantly and at significant range.
Galio's ult CC can easily be interupted and prevented through CCing Galio, which Leona, Udyr, and Xin'Zhao can all force to happen instantly via auto-attacks alone. Galio's ult also has a notably longer cooldown and usually requires comboing with Flash.
Orianna's AA is ranged and benefits from a pretty solid on-hit effect.
Galio's AA is melee, and does not.