Whoa, this was deep. Congrats on writing this.
Thank you.
Looks like I still have something of my old day-essay quality left.
We won't know for sure if he even deserves one pending the events of Union Cross since it's pretty much implied that he is Darkness. All Xehanort really did for him was give him a body and a piece of his heart.
You may be mixing up some stuff here.
No one can "
deserve" a redemption or redemption arc.
A character either redeems themselves or they don't, it depends on if they want to and
do change for the better or not.
Redemption is always something only a character needs and can go through who truly and willingly did some really bad and heinous stuff that can't be mended by a simple apology.
It lies completely with the "bad/evil" character themselves if they can be redeemed or not.
Characters who were literally brainwashed or possessed/controlled by a third power and thus didn't do horrible things on their own will do not need to redeem themselves because they had no control over their actions. In these cases the actual guilt has to lie with the powers doing the brainwashing and/or controlling.
What you may think about is
deserving forgiveness which is a related but different concept. To forgive a person who did bad/evil things however isn't something that can be generalized as it lies with every single person who has had contact with the person who did the bad stuff, with a special focus on said persons victims.
Forgiveness is an individual process so while one person may forgive a remorseful or repentant bad guy another may not even for the same crime.
This is also something that rings true for the audience as i.e. while I personally may have forgiven Ansem the Wise and interpret his remorse and actions to atone as genuine and worthy of forgiveness other people in the fandom may feel differently.
Redemption and Forgiveness get often thrown together or mistaken as part of the same process but they aren't, the first one is completely about the "bad/evil" character and a possible change to
no longer being a bad guy (which doesn't erase the bad stuff they already did) while the second one is about all the people they hurt and those who otherwise got affected by their actions.
In stories with well written redemption and redemption arcs there are often at least a few characters who
do forgive the repentant character in the end, after they have
earned it by atoning and repenting for the misdeeds and repaired damage where still possible, but that shouldn't lead one to believe that Forgiveness is to be an expected
reward for the bad guy-character changing and going through
Redemption.
Being forgiven is a possibility, not a right.
Forgiveness is a gift given by a victim and if the wounds caused by the bad guys' actions are too deep they have every right to
not forgive regardless of what the bad guy does.
Even if Forgiveness is granted, it does not imply an automatic welcome with open arms, that any continued social contact is accepted or that any trust is (re)build between the perpetrator and the forgiving character.