That calculation was done by using the population (size of the deck), number of successes in the population (amount of mana sources), and the sample size, which is the number of cards youve drawn from the deck by the time you reach the target turn
Scion of Draco also fits multicolor decks pretty well, being able to give plenty of combat-related bonuses to gold creatures, and surprise, surprise, Leyline of the Guildpact also helps with these bonuses, extending them to all creatures including the Scion itself
Consecrated Sphinx has great synergy with Arcane Denial and Jace Beleren, it also has great synergy with Force of Will as you ideally want your late game cards to be blue so you can pitch them in the early stages if needed
This doesnt seem like much, but over the course of your average Commander game, this is going to draw you a lot of cards with very little effort