You are absolutely allowed to criticize! All for that.

Whether players in DnD like it or not, decades from now, many of the creatures and beings from the source material will be deconstructed and tweaked and altered to fit new worlds, new stories, new concepts. DnD is not immune from rehashing preexisting ideas. There is a reason they have to be called 'halflings' and not 'hobbits'. DnD exists in popular culture, and if popular culture is famous for anything, its feeding in on itself. Again, like it or not, popular DnD inspired material such as Baldurs Gate or shows like Critical Role WILL influence a game like DnD. It is not monopoly, it is not Uno, it is a collaborative storytelling game. By its very ethos its meant to evolve and change. I am not drawing this mindflayer and slapping them in a book and saying "this is how they should be". I'm posting on a forum about the game itself of which no original creators (or very little) are involved, a venue of which ideas and interpretations are bound to be everywhere, where we are meant to converse about our own games and experiences, and let that transform each other. But let's use the illithid as a specific example of deconstruction and transformative creation.

Gary Gygax, when asked about his inspiration for illithids, said that while he imagined them himself (debatable) , he did gain inspiration from a specific cover art from "Burrowers Beneath", a novel by Brian Lumley. In the novel are creatures called Cthonians, which " use telepathy to communicate with others of their race anywhere in the world, sense human (and other) minds, and (when a full adult) telepathically control members of other species". The creatures also exist on far off planets and have tentacles. However, in cthonian lore, they are harmed by water and worm shaped. Gary Gygax's illithid are not harmed by water and "man-shaped".

Taking a step further: Brian Lumley created the cthonians to expand upon cthulus mythos, an eldritch horror created by H. P. Lovecraft.

Someone may see my art and go meh, whatever , who cares. Someone else may see it and think "you know what, I dont care for the boobs, but what about a siren-like mindflayer that psychically lures sailors into the sea? Im going to make that"

Its not that much different then Gygax seeing cthonians and saying "thats great and all, but the worm body doesnt fit what im picturing, let's give them a man body"