I feel like it's ever so slightly underdiscussed in the fandom that, unlike standard Darkners, the 7 flowers' Dark World forms aren't a result of their histories being personified; they're deliberately constructed personas. One of the ways in which they're "breaking the rules" is by bucking the "No one can choose who they are in this world." sentiment.
Hell, the fact that they take on human forms (well, to varying degrees of success) also plays a part in their rule breaking. Since, at least from our perspective, there has always seemed to be unspoken rules about the depiction of humans in UTDR, or the lack thereof even. Something you often see brought up about Ch 5 is how surreal it is to see more "human" characters in the game! On top of it, there's definitely some intentionality to the fact that each of them are stylized differently; the broader rules of UTDR human character design are mysterious even to them.
In Flowery's case specifically he might even have enough awareness about things that he vaguely understands the way in which humans are supposed to be "special" and is committing a deliberate faux pas by taking the form of one. This naturally clashes against Ralsei, especially since this chapter was gesturing at the idea that they might be taking on a monster form to be more... palatable, I think? Rather than out of any personal preference.
We know that Ralsei personally likes his face, at least. Everything else you said is great though
