I've definitely noticed Gemini's tendency to return the image basically unchanged, but not noticed it being worse or better for images of people. When I tested by having it change aspects of a photo of me, I found it was far more likely to cooperate when I'd specify, for instance, "change the hair from long to short" rather than "Make the hair short" (the latter routinely failed completely).

It also helped to specify which other parts should not be changed, otherwise it was rather unpredictable about whether it would randomly change other aspects.