Syndrome easily is more evil. He killed many heroes, tried to kidnap a baby and turn him into his pawn, attempted to kill literal children, and had zero excuse for his actions. Yes, while being rejected by your favorite hero sucks, it doesn't give you the right to do what he did.
For Lotso on the other hand, he is tragic. Yes, he may have no excuse for his actions, but what happened to him was still awful. He seemed to be generally a good person before his tragedy, and clearly he misses how his life used to be. Yeah, while he has hardly any excuse for his actions, he is still tragic and in my opinion, calling him "fake tragic" is a little much.
Now, yeah, I wouldn't say Syndrome was a bad person before being rejected by Mr. Incredible, but he definitely wasn't a good person.
The Killing Joke can never truly be canon because it’s the story that would occur if Batman and the Joker were to fully play out their game where the Joker goes too far, Batman kills the Joker, but ultimately the Joker “wins” by proving his point (presumably the police would cover up the crime). BUT, since we’ll never reach that point in the same way you can never actually reach infinity by counting… the game will go on and this story will never be canon.