If it’s Ok with you I removed the RS portion of your response and moved it to another post so we can focus the discussion to the topic at hand.
In your response you forgot to include the Problem at the core of each Throughline. This is key to understanding the relationship between the Main and Influence Character Throughlines.
In addition, your description of the Main Character Throughline:
My sense is that the MC is in Activities. I’m tempted to say the concern is in Doing, because Steve’s conflicts all come from the things he does: the fighting, running, helping Bucky escape . . .etc. However a strong case could be made that his overriding concern throughout the movie is to prevent Bucky from being captured and killed. We see that in most of Steve’s scenes from the moment we know Bucky’s in danger right up until the end of the movie.
This describes Steve’s function as an Overall Story Character.
The Main Character Throughline describes those issues unique to the Main Character that exist separate from the Overall Story throughline perspective. Steve is not the only one fighting, running, or dealing with Bucky, etc.
What personal baggage does Steve have that he could carry with him into any other story and how are these uniquely related to Activities and related to him alone?
The influence character through line is in Manipulation. We see Tony trying to manipulate people into choosing his side all the way through the movie (unlike Steve who often warns them that siding with him will get them in trouble.) He tries to manipulate Steve into signing the Accords with false promises (in the pen scene), he uses Spider-Man’s star-struckness to get him to join his side, he gets Vision to try and hide the fact that he’s actually holding Wanda prisoner.
This describes Tony’s function as an Overall Story Character.
The Influence Character Throughline presents a problematic alternative approach that challenges or impacts the Main Character to reconsider his or perspective. These can be through direct, or indirect manipulation that either influences the Main Character or influences people around the Main Character.
How do Tony’s attempts to manipulate specifically impact or challenge Steve to reconsider his point-of-view? What kind of problematic conflict arises in Steve or in the others because these manipulations?
Lastly, a Concern of Doing in the Main Character Throughline suggests a Concern of Playing a Role in the Influence Character Throughline. How do Tony’s manipulations specifically impact and challenge concerns with Being?