If you mulligan, you have better than coin flip odds of opening a card you run the maximum number of copies of
If you play a Tome Scour, you are casting a zero-for-one

Let's see what the rough ratios are for Draconic Domination and how it compares: 54 mana/ramp: 37 lands and for ramp we've got The Ur-Dragon is an enormous one and counts more than anything else since it's always available, Dragonlord's Servant, Dragonspeaker Shaman, Farseek, Cultivate, Kodama's Reach, Sol Ring, Wayfarer's Bauble, Armillary Sphere, Commander's Sphere, Darksteel Ingot, Fist of Suns, Dreamstone Hedron, Frontier Siege, Curse of Opulence, Curse of Bounty, Herald's Horn, Ramos, Dragon Engine 9 "card advantage": Intet, the Dreamer, Niv-Mizzet, Dracogenius, Teneb, the Harvester, Painful Truths, Elemental Bond, Palace Siege, Curse of Verbosity, Herald's Horn, Kindred Discovery, you can count Dreamstone Hedron too but I don't 7 targeted removal: Scourge of Valkas, Niv-Mizzet, Dracogenius, Ojutai, Soul of Winter, Tyrant's Familiar, Rain of Thorns, Frontier Siege, Fractured Identity, and there's also Scalelord Reckoner / O-Kagachi, Vengeful Kami but those rely on your opponents so I don't count them 6 board wipes: Ryusei, the Falling Star, Silumgar, the Drifting Death, Steel Hellkite, Deathbringer Regent, Crux of Fate, Fortunate Few 4 recursion: Teneb, the Harvester, Bladewing the Risen, Palace Siege, Haven of the Spirit Dragon

All of them for free