I hate using the word cancer. It's an ugly word for people that have lost someone to it (and most probably have). So, I'd reserve that word for people who ruin the whole team. Not just as a player, but a person. I do think Kyrie might have earned the term by alienating franchises from fans and hurting his team with randomly sitting out and a weird (if not nasty) attitude. I met Kyrie in a small setting. He was unpleasant. The guy I was with just said "he's not always like that, but he's moody." I hate being around people like that.
I don't consider Zion a cancer, but he will most likely never be a franchise player. He's out of shape. He's constantly conserving energy, so he doesn't make cuts, help on defense, rebound, etc. Even if he were in shape, his body type is not conducive to his playing style. His injuries will most likely continue. If I were the New Orleans GM, I'd trade Zion. I'm not sure if the Knicks have the assets, but I can see them totally overpaying.