The discount which Gargos provides is significant, especially for Hydras with X in their mana cost, but Polukranos, Engine of Ruins ability to generate tokens also shouldnt be underestimated
You know what they say double the doubling is quadruple the fun
This will likely make it so that one of the lands will be the same color as your commander's identity, which tends to be more useful than any color, and it is one of the best lands that allows for easy mana fixing in any deck
When you do, itll be saucy
White: Summon: Knights of the Round, Good King Mog XII, Ixion, Yojimbo - I still have no idea how to evaluate these and being unable to try these out hasnt helped
Plus, when mass removal happens, which is always a threat, you are able to draw two cards for your trouble