For example, Heimdall, in pretty much everything except the MCU, is white.
I mean, one of Heimdallr's descriptions is "the whitest of the gods", and has his origin in Northern Europe, so I don't know why typically depicting him as white should be a shock.
Because all that stuff about artistic freedom apparently doesn't matter when it means making a character black that they'd prefer to be white.
Hypothetical: MCU starts introducing New Warriors characters at some point in the future, would you be OK with it if they cast a white woman as Hummingbird? Do you imagine it would go without upset and outrage from certain corners of the internet? In case you aren't familiar with that character, in the comics she's a Mexican girl and also probably an incarnation of Huītzilōpōchtli (the Aztec deity of war, sun, human sacrifice, and the patron of the city of Tenochtitlan).
ETA: It's a bit dicier when it comes to recasting pre-established characters,
...and you'll notice most of the times you see significant bitching, it involves casting pre-established characters in a way that doesn't at all resemble their existing descriptions. Hell, there wasn't even much complaint about black Nick Fury, mostly because there was an extant black Nick Fury (albeit from a different version of earth than most of the MCU is set in).
That being said, I am reminded when Ghost in the Shell became an American movie starring Scarlett Johansson.
Was opposed to that too. I mean beyond the degree to which I'm opposed to live action adaptations of anime, because they have a general habit of not being very good.
Green Lantern? Robin? Clayface? It happens all the time. But for some reason we get far fewer moans when it's a white dude passing the mantle to a white dude.
Green Lanterns have been multiple races, as well as aliens of basically any description. Also Carol Ferris, Katma Tui, Arisia Rrab, Jennifer Lynn-Hayden and Jessica Cruz for notable female Green Lanterns. Y'know, I'm now tempted to start up the Scribblenauts DC game and see if they're among the 40-odd Green Lanterns that game recognizes. Of course for GL this isn't super surprising, since it's akin to talking about how the mantle of "works for the police" gets passed around, as GL is essentially a job title rather than a single identity.
Robins either age out of the role and take on a new identity to get out of Batman's shadow (Nightwing, Red Robin, Spoiler/Batgirl), or they...don't survive long enough to get there (such as being beaten to death with a crowbar by the Joker).
Clayface is admittedly all over the place, although about half of them derived their powers from either experimenting with blood or DNA from another version of Clayface (usually Hagen, or someone who's powers came from Hagen) or in one case being the child of two different versions of Clayface (Cassius). Notably, Cassius' parents met because a villain group composed entirely of versions of Clayface called the Mud Pack formed and both of his parents were members.
Also, at least one woman has been Robin (who later fakes her death and then becomes Spoiler) and at least one woman has been Clayface (Cassius' mother).
Also notably all your examples are DC. Speaking of DC, a movie or (another) series about Static could be cool - for anyone not familiar he's a black superhero with electrical powers. Maybe have him show up as a side character in another movie first to introduce him to people who's familiarity with DC comics is limited.