Reading List (Super behind but reading them nonetheless):
DC: Currently figuring that out
Marvel: Read above
Image: Killadelphia, Nightmare Blog
Other: The Antagonist, Something is Killing the Children, Avatar: TLAB
Manga: My Hero Academia, MHA: Vigilanties, Soul Eater: the Perfect Edition, Berserk, Hunter X Hunter, Witch Hat Atelier, Kaiju No. 8
That's the thing. Back in the Golden Age of comics, "invulnerability" meant immune from all physical harm. In fact, in Black Adam's first tussle against the Marvel Family, neither Black Adam nor the Marvel Family could harm each other, even when they were punching each other. Now, being "invulnerable" simply means that a person with this power is immune to things that can harm a NORMAL person. And certainly, we've seen Black Adam do damage to Billy whenever they fight each other.
And that's where the bone of contention lies. Some feel that Billy should have been immune to the Scarecrow's toxins, even though the dialogue explicitly stated that a) the Scarecrow states that he is NOT some ordinary street thug, and, b) that his latest fear toxin was something new. Nothing in the book reads "bad writing", when you could easily pull examples where Doctor Sivana's use of science can harm even Billy, so why can't the Scarecrow, since he, too, is a "super-villain"?
And personally? Just because the hero has "magic powers", that doesn't mean either "super-science" or even "weird science" can't be a counter-measure to "magic".