@fly2spring Almost all stories have the MC being the Protagonist. So unless you are writing something non-mainstream, you can think of them as the same. There is no Protagonist Throughline, Protagonist is a role that is assigned. You can select which one of your characters is the protagonist on the Character's page. There is a TYPE dropdown.
The OS and MC are different points of view, you need all 4 throughlines(POVs) for a grand argument story (GAS), that is kind of the whole point of using Dramatica. Though, you are the writer, you can leave throughlines out, it would just create a smaller story (Tale) that likely would not be as good.
The Overall story is what everyone in the story world is dealing with (Ex. The Immigration Apocalypse), the MC story is set within that larger story and told from a different perspective... the personal perspective (Ex. Donald Trump with only a baseball bat and a can-do Amerikan attitude to save the world... one dead illegal immigrant at a time). The MC is an avatar for the audience member to step into and experience your story. The audience can't relate to the Overall story on that personal level.
Free showers will be offered after the movie for those wishing to wash the Trump Juice off themselves as soon as possible before it stains their psyche.
No illegal Immigrants were harmed in the making of this film.