I wrote a few stories with all 4 throughlines, but I kept feeling like I was missing something (other than, you know, talent).
I claim no expertise, but I suspect I was missing a MC TL "personal opponent" who:
A) is not the IC (or a co-IC) and
B) is not strictly an OS logistical opponent.
Basically, someone that helps to demonstrate MC growth. I'm thinking of characters like:
Calpurnia - Scout's personal "nemesis;" their interaction is neither OS nor RS; Scout views/treats her more equitably at the end of the book (not movie).
Dorothy Gale's mom - Dorothy gave her grief at the beginning, but appreciates her at the end. She's not an IC and isn't in the OS significantly.
Michael Clayton's estranged brother Timmy - the DUG analysis for this movie is what made me think of this concept when Chris Huntley asked, "What's a really clear signal that Michael resolved his personal angst? He reaches out to his estranged brother."
In each case, the MC growth was demonstrated by how the MC treated someone. Forgive me if this is mundane, but it was a joyous breakthrough for me (someone who naturally tends to think of plots more than characters & relationships).
Is such a character necessary? I suspect not. The "someone" could be himself. You could argue MC growth could be communicated solely by the MC himself with no interactions with another character at all, but I think that method is damn difficult. That's what I've been trying to do without realizing it. Things like, "he was on the bottle, then struggled with it, then got off the bottle at the end." It risks being either too subtle or too melodramatic (edit: for my amateur writing skills; other writers can probably do this well).
Also, you could argue that you don't have to make up an additional character to show MC growth, as the MC TL opponent could be a pre-existing character with a role in the OS. But that makes it difficult to separate the MC's role in the OS from the MC TL.
So, long story short, I'm going back to add a separate non-OS character to help me demonstrate MC growth more clearly.
PS If a term doesn't exist, I nominate Calpurnia! Or Timmy Clayton!