Marvel Studios origin films typically begin with a hero rising to take down a villain possessing the same abilities they do. Iron Man took on Iron Monger, Captain America battled Red Skull, Ant-Man tangled with Yellowjacket and the list goes on. But that wasn't a symptom of happenstance, it was strategy, as explained by studio President Kevin Feige.
"Clearly we will get to that [non-doppelganger match ups]… You want to have characters that inhabit the same world when introducing a new world, a new mythology for lack of a better term. You want to explore that as much as you can," said the MCU mastermind. He went on to explain his strategy using Doctor Strange and Kaecilius as an example, "....when you’re teaching an audience about sorcerers and that reality and you’re going to talk about the past anyway and you’re going to get into their history anyway, much better to tie-in your bad guy with that instead of laying all this groundwork of parallel dimensions and sorcery and say, by the way, a meteor hit on the other side of the world, it went under the water, and this evil thing developed. What does that have to do with magic? Nothing… That’s not the way we’ve developed them up to this point."
However, moving forward, with characters firmly established, the plan will be to break the mold and have more dynamic match-ups moving forward. "Needless to say as more characters encounter each other in other films they’re certainly going to be up against things that they don’t know anything about and have no comparable to." So if there's another solo Iron Man movie, perhaps he'll tangle with a magical adversary? Or perhaps the next Captain America film will feature Steve Rogers addressing a threat that he can't stop with his fists?