At some point you have to take a work at face value and see what it is trying to say.
Is the breakdown of monarchy actually relevant to the themes and messages presented in Sailor Moon? No, not really.
So focusing on the Moon Kingdom monarchy and the ethics there of is sort of... besides the point. The Moon Kingdom is a fairy tale, not a reflection of reality.
I’m not actually interested in the tax policy of the Moon Kingdom, you know?
Now, is it *cool* to look at works in various ways? Sure! Are some people interested in the tax policy of the Moon Kingdom and want to explore what that would look like? Sure! And honestly if you want to explore the ramifications of idyllic fairy tale monarchies on the real world, then that’s really cool too!
But if you are looking at a work to understand what it is trying to say with the text itself, then you need to take some of its premises at face value. Usagi and the Sailor Scouts being the Good Guys is one of those premises.
And really the “Usagi is secretly a princess from the moon” is just a part of the escapist fantasy for most little kids watching more than it has anything to do with actual themes of monarchy.
There is a lot of value in being able to look at a text from various angles. And it’s perfectly okay to use a text and concept as a jumping off point for other explorations.
But the problem comes when people say that Usagi was definitively a villain in Sailor Moon, or that say Steven Universe with themes of family and conflict resolution is excusing genocide by not destroying the Diamonds. It misses the point of the fantasy. It misses the important themes, the lessons and point of the show to look at it like that.
Basically: reinterpretations are cool, but you gotta know how to take a work on its own premises too.