Getting back to marvel, the simple fact is that the majority of their super heroes are white males. There's no getting away from that.
Of course there is. We've seen abundant cases of white characters in the comics being played by nonwhite actors onscreen -- Eartha Kitt as Catwoman, Billy Dee Williams as Harvey Dent, Michael Clarke Duncan as Kingpin, Kristin Kreuk as Lana Lang, Sam Jones III as Pete Ross, Alessandro Juliani as Emil Hamilton, Phil Morris as J'onn J'onnz (whose human disguise was traditionally white in the comics), Dania Ramirez as Callisto, Kerry Washington as Alicia Masters, Samuel L. Jackson as Nick Fury, Idris Elba as Heimdall, Maximiliano Hernandez as Jasper Sitwell, Laurence Fishburne as Perry White, Chloe Bennet (nee Wang) as Daisy Johnson, Henry Simmons as Mack Mackenzie, Vondie Curtis-Hall as Ben Urich, Michael B. Jordan as Johnny Storm, Candice Patton as Iris West, Keiynan Lonsdale as Wally West (yes, he became black in the New 52), Ciara Renee as Hawkgirl, Angelica Celaya as Zed (
Constantine), Mehcad Brooks as Jimmy Olsen, David Harewood as Hank Henshaw (and J'onn again), B.D. Wong as Hugo Strange, etc. We've had half a century of actors "getting away from" the whiteness of their source characters, and it's an everyday thing by this point. It's just that, for the most part, it's still limited to supporting characters or members of an ensemble, rather than lead characters. That glass ceiling still exists.
But for most lead characters, there's no reason why they
have to be white, any more than a live-action Jimmy Olsen has to be a redhead or Barry Allen has to be blond or Wolverine has to be 5'3". Steve Rogers would probably have to be white given the era he comes from. Black Widow, probably -- not a lot of Asians, Africans, or Latinas in Russia. I've heard it argued that Bruce Wayne or Tony Stark would have to be white because they come from super-rich forebears and there weren't any nonwhite billionaires back then -- but there's no reason a white Thomas Wayne or Howard Stark couldn't have had a mixed marriage and a biracial son. Clark Kent could presumably have looked like any human ethnicity (and indeed he has been played by the quarter-Japanese Dean Cain). Wonder Woman's an Amazon, so realistically she should be something like Turkish or Central Asian (Amazons weren't Greek, they were enemies of the Greeks). Peter Parker's a lower-middle-class teenager from Forest Hills, so he'd actually be
more likely to be nonwhite, given current demographics. And so on.
And I highly disagree with your opinion about the Avengers characters not being well known because I knew who they were before the movies and rarely read comics. Those characters were chosen because they wanted to build a series of movies that culminated in the Avengers. Black Panther and Captain Marvel werent needed for that.
They weren't completely obscure, no, but they were seen as B- or C-list characters at the time. People maybe remembered the '60s cartoons and the cheesy theme songs, or maybe the embarrassingly kitschy attempts to adapt Captain America to TV in the '70s and film in 1990, but they were not seen as A-list heroes on the level of Spider-Man or the X-Men. That's
why Marvel still had the rights to them -- because they were the characters that other studios hadn't cared enough about to snatch up the rights to when Marvel was broke and selling off the good china. So you're getting the cause and effect backward. What happened, according to the story I've heard, was that the folks behind Marvel Studios took a look at what they had left over and realized, "Hey, you know, these characters we still control just happen to include most of the key Avengers. Let's take advantage of that."
Why weren't they needed? They've both been Avengers in the comics for years. There's really nothing that says that the Avengers only had to be Iron Man, Captain America, The Hulk, Hawkeye, Thor and Black Widow. I know that is the classic group, but I don't really think it would have hurt anything if they had switched out one of the guys for BP or Capt. M., or even just added one of them to the team in the first movie.
Actually the
founding lineup of the Avengers was Iron Man, Thor, Ant-Man, Wasp, and Hulk, with Hulk leaving and Cap joining soon thereafter. That lineup then gave way to "Cap's Kooky Quartet" of Cap, Hawkeye, Quicksilver, and Scarlet Witch. Black Panther and Vision joined in 1968. Black Widow didn't join until 1973, a decade into the series. Carol Danvers (then known as Ms. Marvel) and Falcon joined in 1979, War Machine in 1984.