Well if you list out a lot of his actions, him turning good is a bit of a hard sell since he slaughtered entire races without any remorse, then he gets a suger mamma for a wife who still manages to remain a hot piece of ass and gives him two kids, all while putting up with his selfish drive to upstage someone he's always considered lesser than him. He's still a fun character, for sure, but I can see why people do have trouble with his redemption compared to other rival characters.
As for XANA, I just feel like it was best when it was a force of nature that was beyond any comprehension other than it's crazed schemes of robot armies and subjugating humanity. Brainwashing though is a little hard to wave since the individual still did a lot of traumatic things. If we absolutely had to have XANA turn good, and still do a lot of bad shit, I could maybe see it getting killed, but having a backup/copy made that gets to live the life that it never got to have.