It's not my criticism, it's one I've heard and sort-of understand considering D&D came out first and you can see the influences on WHFB. It definitely has original stuff, chiefly being the Empire's Holy Roman influence, the Lizardmen, Skaven, and Chaos armies. But the three elf races, orcs, dwarves, and Bretonnia lack some originality.
It's a terrible criticism made by ignorant people who you shouldn't be listening to because now they've embarrassed you by having you repeat it.
D&D is the exactly same thing - a synthesis of various fantasy elements in a somewhat clumsy way. Also, Warhammer is far, far less derivative from D&D than you seem to think. It's separately derivative from similar sources - it takes far more from Michael Moorcock, and takes stuff directly from Tolkien, rather than filtering it through a D&D lens. A good example are the Orcs, which are derivative of Tolkien's Orcs, not D&D's modified Orcs and later became their own wildly wacky almost-sci-fi thing. They're vastly better developed and more original than anything D&D has ever done with orcs or goblins (though Eberron's goblins are pretty great). I mean, they develop from spores for god's sake. They're sentient fungus. And you're claiming they derive from D&D's grey-skinned pig-men orcs from the 1970s? No. Just no. They're smarter than those, too, more like Tolkien's Orcs again.
Bretonnia isn't derivative of D&D, and you're ignorance about the origins of Bretonnia is showing here. When it was first added, it was basically "France immediately before the Revolution", with poncy 18th-century-style Aristos and a rebellious underclass. Later they retcon'd into into a darkside version of the whole King Arthur deal, with a strong French flavour. There's nothing in D&D particularly like it, and it's not derivative of D&D.
In terms of Elves and Dwarves, D&D is in many cases derivative of Warhammer. But both are directly pulling from Tolkien. Still, a lot of the visual design D&D post-1990 has used for Elves and Dwarves is in fact derivative of Warhammer. Warhammer certainly isn't derivative of D&D here - their Elves and Dwarves have far darker, more Silmarillion-esque histories, and neither is "Lawful Good".
None of it is "truly original" (even all the Chaos stuff is inspired by Michael Moorcock's books, albeit really heavily developed - Moorcock is also why D&D has Lawful and Chaotic alignments, note, and the planar structure it does), but the idea that it derives from D&D is laughable (spurred to exist by D&D becoming popular, perhaps, but that's different), and the idea that that criticism makes any sense in the context of D&D, which is exactly the same mish-mash of this and that, is just bizarre.
Orc-wise, let's talk who is derivative of who:
Orc, D&D, 1977 -
Orc (Dungeons & Dragons) - Wikipedia
Quite clearly pig-men, which they are still described as in 2E, and depicted as, and have grey skin.
Orc, Warhammer, 1986 -
Blood Bowl - Wikipedia
Already by 1986 Warhammer Orcs (seen left) are the classic short-nosed, musclebound, green-skinned orcs we are used to in various things.
Orc, D&D, 1993 -
2e d&d | Tumblr - The image on the left, from Iuz The Evil, 1993. Still with the pig-men.
Warhammer Orcs haven't changed since the 1986 image, not significantly (and indeed looked like that earlier in the 1980s, but I wanted an image with a hard and undeniable date)
Yet let's see how D&D Orcs looked later:
Orcs were a race of humanoids.[4][5] While they differed greatly, orcs shared certain physical qualities. Orcs of all kinds usually had stooped builds, grayish skin, and coarse black hair, with low foreheads, reddish eyes, and faces of porcine appearance that featured large lower canines similar...
forgottenrealms.fandom.com
Wow even better they show 1E/2E/3E/4E/5E progression (the 2E one is from 1994, note, when the change to copy Warhammer Orcs had begun). You can quite clearly see that D&D Orcs are derivative of Warhammer Orcs, not vice-versa.