I'm going to refrain from commenting on the other points because they're all clearly stated and, at a certain point, my inability to fully wrap my head around the is my own personal issue and not necessarily illuminating for anyone else.
Since you asked . . .
I'm assuming this second storyform within the movie has the following throughlines and domains. I fully expect you to expertly show these as flawed, but do know that I've tried at least to follow the principles you've laid out, however flawed my conclusions.
OS of manipulation (Zemo manipulates everyone into self-destructing: "An empire toppled by its enemies can rise again. But one which crumbles from within? That's dead... forever.")
RS of activity (Almost every scene with Cap and Bucky in it is about the two of them fighting either against each other or together: note the big end clash against Tony where they fight seamlessly together as brothers-in-arms).
MC of situation (Steve is a man ripped from his own time, forced to live in an era where nothing is familiar and everything integral to his life and experience is at odds with everything else around him. His friends are all dead except for Peggy who they make a big deal of killing off in this movie, and Bucky. Take Steve out of 2016 and put him back in his own time – or even back in the ice – and he'd be unstuck.)
IC of fixed attitude. You and I have discussed on a number of occasions that it needn't be the IC who is themselves trying to push the MC to change, but that the very fact of their existence or the way others see them can create that pressure. Everyone believes that Bucky is an unredeemable assassin – even Bucky believes that at times. This constantly challenges Steve's view of his oldest friend as a decent and heroic individual.
To now answer your question directly:
Steve's perspective is of the Bucky he knew, and the utter conviction that no amount of brainwashing and conditioning – or even all the terrible things Bucky's done – can change the essential nature. Bucky's perspective is coming from the memories of having killed all those people ("Do you even remember killing my parents?" Tony asks. "I remember everyone I killed," Bucky replies.)
Bucky changes to adopt Steve's point of view. He sees how different he is from the other Winter Soldiers that are still in the tubes at the secret compound (the ones Zemo kills) Bucky goes from believing he has no value as a person, to looking towards a future where maybe he can overcome the terrible controls that were put on him – as we see in the scene in Wakanda.)
You might – might – choose to argue the opposite, I suppose, and say that since Bucky goes into the tube at the end and Steve accepts his decision that it's Steve who's perspective has changed, and he now sees the situation through Bucky's eyes as someone who can't trust their own mind.
Neither of these perspectives is about the Civil War or Zemo's broader manipulations. Both of those aspects of the OS are like looking down at a chess board: who is on what side, what pieces are being moved. Steve and Bucky's perspectives come from the "I" (I'm stuck in the wrong time and I've lost almost everything that was integral to me) and the "You" (The way you insist that the person you were died threatens to take away my one connection to the past).
Let me know if any of that is actually a reasonable application of Dramatica principles!