In the case of White Knight, another factor also plays a role: nostalgia
Taking a slightly slower and more methodical approach to Voltron can be rewarding, and pushing Breena into those Swiftfoot Boots is an idea with a lot of merit
It also can continue copying creatures, gaining their power, toughness, and abilities every turn
Its also interesting in Eldrazi decks that look for colorless expensive threats
Once the Seer is legal though, it should increase the power level of the deck dramatically
Cards that dont require additional mana, like Sigardas Splendor and Cosmos Elixir solve this, but ultimately are a touch unreliable, especially in light of other card draw options in white