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Ros-mei is a social climber who didn't want to end up as a concubine. She still wanted a reverse harem of muscular men. Big breasts would help. She probably mentioned it to Insight as a slightly jealous statement of praise, hoping the compliment would bring them closer. 

Insight, a duplicitous woman, mocks her subordinate due to her inner need for the validation of her superiority in her competitive world. It shows a bit of realism in her character. Still, she's not a truly terrible person, she keeps these thoughts to herself while treating her squad well.