I do think that Prospero has wronged both Caliban and Ariel. Prospero arrives on the island after having been usurped by his brother Antonio, and he feels wronged by his brother's betrayal. However, Prospero does not extend these feelings beyond his own situation, and when he arrives on the island, he takes Caliban as his slave and makes Ariel do his bidding. Prospero tells Caliban that he has done him a favor by taking him under his authority, suggesting that Caliban had an uncivil life with his mother Sycorax the witch. Similarly, Prospero tells Ariel that he saved Ariel from Sycorax and that now Ariel should repay this favor by doing magic. Prospero promises on multiple occasions to free Ariel; however, each promise is followed by a request for more magic. So, Prospero in some ways is not any better than Antonio because he feels justified controlling the lives of both Caliban and Ariel and thus deserves his suffering.