I don’t agree. Jane Fairfax deceives her aunt, her grandmother, everyone in Hartfield, and her future father-in-law and his wife. She enters into a secret engagement knowing Frank’s aunt would disapprove. Fanny isn’t capable of such deceptions; she would feel duty-bound to tell, ask permission, and withhold her consent until permission was granted. It is a climactic moment when she stands up to her uncle Bertram and refuses to marry Henry. In that action, she remains true to herself and to her moral compass (knowing Henry is a rake, and disapproving his behavior with her engaged cousin).
As for Frank, he’s hardly the immoral rake Henry Crawford is; he’s selfish, vain, deceitful, and neglectful of the duties owed his father and step-mother, but hardly a rake.