The idea that earth ponies didn't have magic in G4 is a retcon. During the S4 finale, Celestia flat out says that without their magic, earth ponies wouldn't be able to tend the land. They always had magic, it was just more passive than the others. Theirs granted them enhanced endurance, strength, constitution and an innate connection to nature. I'd be fine if G5 expanded on that with their new grow magic, but pretending they never had any at all is disingenuous.