User blog comment:IamJakuhoRaikoben/Sorcerer Magazine, Issue 41: May 2015/@comment-1153699-20150602132933/@comment-25111584-20150602202629

Aw, c'mon Raven! You're taking extreme cases into consideration. Mavis stated that Cana had great latent potential. This is of course an interpretation, but I take that to mean that Cana using Fairy Glitter is using her full power, the maximum she can in her life. She's Gildarts' daughter, it's in her genes! Mavis stated as much too. When she is fully trained, why can't Cana be stronger than Jura? It might take years, but she could do it. Just think of Fairy Glitter as a cheat, just like Etherion and Flame of Rebuke were for Natsu in attaining Dragon Force. :P

Not to mention that Cana cannot use FG on her own, she needs to get it from Mavis. You shouldn't even consider that case, Raven! ಠ_ಠ