I also vehemently disagree with the concept that Chaos = Random = Disordered = Whatever.
The Law and Chaos breakdown is more along the lines of structure vs personal freedom and desire.
And part of personal freedom is determining your appearance. More homogenous, lawful societies encourage conformity in many ways, including visual appearance. Devils embody law so they’re more uniform in appearance, in my approach. Devils should look like legions and well organized armies, with “uniforms” that make them look fairly similar to one another. Not to the extent that all Devils of the same type are identical in the way Modrons are, but extreme lawful structure encourages conformity. Demons should be the opposite, IMO. No two demons should look exactly alike. This is part of why I dislike the Blood War art
@Bae'zel posted earlier and do like the Descent into Avernus Demon art
@dave2008 posted. The Bearded Devils are slightly more organized than the Dretches, but all of the Dretches look identical and are still mostly in order. But having Demons differ in appearance depending on which Demon Lord they serve is interesting, and even then the demonic horde looks properly chaotic.
And like
@Ruin Explorer said, D&D’s Demons and Devils need more visual distinction. If you were to explain the differences between Demons, Devils, and Yugoloths to a new player and then show them the art for the types of fiends and ask them to sort them by category, I think they would get most of them wrong. Bearded Devils are just purple dudes with green tentacle beards. Spined Devils and Nupperibos look pretty demonic to me. On the other hand, Quasits and Nabassus look pretty infernal to me. What part of the Marilith’s classic visual appearance points to them being demons? The new art looks more demonic to me than the old one. I always thought the old Marilith looked like it fit in more with the Yuan-Ti.
Also, like why were Mariliths (mostly) topless women from the waist up before? What purpose did it serve? They weren’t even sexualized in a way that makes sense for demons, like Slaanesh’s Daemonettes in Warhammer.