The two-protag dynamic

A friend once observed, while critiquing one of my novels, that I appeared to be using one of the pair of main characters as a whipping boy. Bad stuff always fell worse on the one character, not the other, though the other is the one who instigated the situation. The other, in fact, often was being forced to watch as a punishment; the bad guys explicitly damaged the one to hurt the other. Which called into question why the whipping boy was there at all - what was their purpose, aside from soaking up punishment I subconsciously did not want to inflict on my chosen character? A very good question.

(An excellent critique overall, and a good friend for being willing to pull no punches. I needed to hear that.)

In revising the current novel, Switchback, it occurs to me that I'm still exploring the dynamic between two main characters, one of which inevitably becomes my favorite by the end of the first draft. I'll probably always be re-learning the lesson of that earlier critique, I'm afraid - I've done it again here, trapping the secondary protagonist and leaving the primary character to dig him out - but I am at least aware of what I've set up (and why robbing that character of agency is not a good thing for either character or story).

So here I am, on rewrite, considering that secondary protag. I can't do the obvious thing and combine the two characters, not in this story; it needs to remain a story about two brothers. What I can do, though, is build in goals for that secondary character. What is being trapped doing to him and his goals?

What I can't do is consider the scene solely from the standpoint of how it affects my primary character.

I'm going to go make some pound cake and think on that.