The way I see it, Jaime has paid his penance for tossing Bran from the window. He has lost his hand, which was essential for his swordsmanship, his claim to fame. He, like Bran, is now a cripple. We can stop dwelling on that, and allow him to grow as a character.
It would be justice if he was actually punished for his crime of attempted murder or if it had been Robb who have taken his hand.
No, Jaime lost his hand because he pissed off Locke instead of shutting up like should have after protecting Brienne.
Two totally unrelated events.