That kind of arc works and produces a satisfying redemption. However, it sadly wasn’t what Lucas wanted to tell and the saga’s story suffers as a result. But hey, I buy Vader’s redemption infinitely more than I buy something like Snape’s redemption.
Really? What is it about Snape’s redemption you find unconvincing (bearing in mind I’m not the biggest Harry Potter connoisseur in the world, but I do like the series)?