I feel like the biggest problem Marvel has is the repetitive "evil twin" narrative of their films, where many of Marvel's villains are just nasty copies of the heroes.
Iron Man vs. Monger/Whiplash (Arc Reactor powered armours), Cap vs. Red Skull/Winter Soldier (Nationalist Medically enhanced brawlers), Ant-Man vs. Yellow Jacket (Shrinking dudes), and the upcoming Doctor Strange vs. Baron Mordo (Sorcerers taught by the same teacher). Even Thor vs. Loki (Advanced science that looks like magic but is never explained), though they are the most different in their twinship, which is why Loki is worth keeping around.
Now, the Avengers films do a great job of changing that up, so did GotG. And Civil War could, too.
It's not just Marvel; DC had exactly the same problem with Man of Steel... Zod and Clark were even wearing virtually the same damn clothes.
It's a crutch that is the simplest way to tell an origin story (which Marvel said sis a business they were getting out of, yet Doctor Strage clearly is), but it's also the simplest way to tell any hero's story.
And if anything is going to get in the way of the Golden Age of Superhero's big screen longevity, it's that.