Ruiz doesn’t the frame for cruiserweight or light heavyweight even if he got himself in excellent shape
Some people are naturally soft. You see that with Mexican genetics. Even when Ruiz was a young amateur he was like he is now. I think if he tried to lose weight he would be weak and slow. He has no issues with mobility, power or stamina so why exactly should he lose weight? Having 270 pounds behind his good movement could potentially be a large reason why he has an excellent chin and good power.