I don’t know Proximus so I can’t judge him, but the Chameleon isn’t perfect. She’s not a terrible villain, but her backstory could have worked maybe if Mantis was there and said something like “yeah, many people didn’t believe in me due to my size as well”.
The fact this doesn’t happen means that as far as we know Mantis didn’t have any problem and thus the Chameleon’s backstory doesn’t work very well.