She makes the list thanks to enabling a bunch of new strategies in black that dont have to rely on classic linear wincons
Source: Comment on Reddit Build a shell that ramps hard (for Ornate Imitations) or and/or loops ETBs (for Fear of Change): Green mana rocks, ramp cards, Overlord of the Hauntwoods, or treasure to push to X = 9 quickly
Before this change, Wizard Mentor was a first pick card which could save your creatures from creature kill spells, allow you to reuse the bevy of 187 creatures in the format (Ghitu Slinger, anyone?), and at worst case scenario allow you to play emergency defense
Of course, this all comes down to the individual components of the decks and whether the strategies excite you, but I think this is an above-average offering
Bighorner Rancher's second ability is a mana ability