It's locked in Feige's head.
As others have pointed out, it's similar to typical 80s films and most blockbuster films. Built upon the heroes journey. The difference is Marvel likes to have their characters be slightly light and alloof. Humour is also injected at regular intervals. The Russos themselves even said that Feige likes to hear the audience laugh every 5 minutes or so as that is an indicator to him they are enjoying the picture.
Ignore the different dressing, but the formula also incorporates the fact that the MCU (like the comics themselves) has a house style they follow in that most (Not all) often have similar colour palettes, edited in a similar way, similar choreography, same type of humour, characters often deliver one-liners.
The Netflix shows had a formula that you can see throughout each show regardless of how it's dressed. The films do too (with exceptions such as Raimi, Gunn, Coogler to a degree).
But if Marvel just followed similar film formulas, they'd look like every other film that used that formula. They don't. When you watch a Marvel film, you know you are watching a Marvel film without even seeing the logo due to how it looks and sounds.