Im a fan of protection spells that leave your board stronger than they were before the effect you needed protection from, and thats exactly the Mutational Advantage youre getting
The deck felt unbeatable, and though WW strategies are traditionally thought of as "bad" in Cube (see Andy Cooperfauss' Rebel errata as a possible fix), I haven't found this to be the case with my current build: My most recent post in the "3-0" thread illustrates the power of what a good friend calls "Death and Taxes cards." Check out this lineup of 1's: Champion of the Parish, Champion of the Parish, Dryad Militant, Dryad Militant, Loam Lion, Loam Lion, Figure of Destiny, Student of Warfare, Isamaru, Hound of Konda, Mother of Runes, Weathered Wayfarer, Wild Nacatl See
For instance: Creatures (20) Lands (25) Spells (15) Sideboard Katzs deck is not naturally well set up to get its hand down low enough to make great use of the Scroll
In constructed you could have multiples of these which you cannot in cube and that does detract quite a lot from its potential value