With more card draw, you can control games with cards like Organic Extinction, play huge spells like Wake the Past, and get your big creatures and planeswalkers like Brudiclad, Telchor Engineer and Ugin, Eye of the Storms more reliably
Meanwhile, The Scarab God slowly drains your opponents the more Zombies you control, while also giving you a cheap way to steal your opponents creatures and turn them into Zombies
Pair this with a restrictive mana cost of three different colors, and maybe Tamiyo wont see as much play as her power level suggests
Any cards with one or more of these types in their type lines count as historic cards
The difference is a bit jarring
Oh, you meant the actual smallest cards