Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Considering that Galio manages a taunt,it gives him 30% AD absorbtion,which means he takes 70% damage only.
The fact is,that maokai's ultimate adds this damage absorbtion,by 25%.
Galio take 56% damage when using ulti. Which means damage is reduced by 44%
Sion's ultimate heals,in addition when teammates are nearb while he is atking.Which gives Galio extra hit points on tanking during the taunt.
Corki and Kog'Maw both shred armor.Plus they have the best harassement tools in the game,their ultimates.
Fact is that this team can just watch Kog'Maw and Corki harassing in a long range the other team.And whenever they decide to pop in,they are supposed to be litteraly destroyed by galio's ultimate,Maokai's CCs aswell as Sion's damage.