I've yet to see a good argument why Doctor Who doesn't count other than it's a niche geek thing in America. America's not the whole world.
Dick Cheney scowls at you.
It's cornerstone of popular culture in Britain, mainstream and massive.
You provided the answer: you say its a
"cornerstone of popular culture in Britain, mainstream and massive," but that is not true anywhere else. I've traveled enough to know images of Darth Vader, Luke Skywalker or Shatner's Kirk and Nimoy's Spock are instantly recognizable, even to those who do not count themselves as fans. That is an example of mainstream and massive, as its not isolated to a small group who needs to be "in on" the production in order to be recognized for its characters, history, etc.
I seriously doubt the average person on streets of the world would--on the spot--recognize images of Tom Baker, Sylvester McCoy, David Tennant, or Colin Baker as the Doctor.
And does no one want to comment on my nomination of Anderson/APF/Century 21 as one of the greats?
No.
At this point Trek and Wars have been around for decades, and have a pretty solid place in popular culture, and the MCU is nowhere near that level.
All true. The MCU is a franchise, but its not sci-fi, and in terms of cultural impact, mass productions alone do not mean its relevant. Its just a well-funded series, but I do not find it difficult to argue that in 20 years, most of the MCU will seem like a blur, in part thanks to the "maxi-series" approach to linked films, with only a small handful standing out as solid productions.
If you mean the comics, then I'd have to say DC is slightly ahead of it. Prior to the MCU, Spider-Man was really the only Marvel character with a solid place in the overall pop culture, while DC has both Superman and Batman, who are both probably even more well know than Spidey.
Again, true. Spider-Man is one of the few comic characters to transcend the native medium, but Superman and Batman jumped to modern myth status long ago, at least where superhero fiction is concerned.