After all, the best way to answer a problematic card is to never let your opponent cast it in the first place
Selvala, Heart of the Wilds Selvala, Heart of the Wilds activated ability is a good source of both ramp and mana fixing, even on its own
Though not a Human itself, Sigarda is a 4/5 Angel with flying for four mana that offers its control and Humans they control with hexproof
The deck features a ton of different ramp spells to help do this: acceleration effects (Battery Bearer, Cradle Clearcutter), Land fetch effects (Bushwhack, Floriferous Vinewall), and spells that generate powerstone tokens (Geology Enthusiast, Argothian Opportunist, Stern Lesson)
Kuja, Genome Sorcerer/Trance Kuja, Fate Defied stands in to represent any effect that results in a black wizard and contributes extra damage with your noncreature spells
Grafdiggers Cage Grafdigger's Cage has lots of utility