And are you sure that what you perceive as a lower quality image is related to the race of the astronaut at all, having similarly tested it 20 or 50 times?
Because concluding that Google is doing a "hamfisted" job at ensuring diversity is going to require a lot more evidence than your description of just three images. Especially when we know AI image generation produces all sorts of crazy random stuff.
Also, judging AI image generation by its "historical accuracy" is just... well I hope you realize that is not what it was designed for at all.