No matter how obvious it may seem, an argument is an argument. If it is something you want to write about, by all mean, do so !
Now you have to find how to formulate it in Dramatica terms. To do so you must first deduce who is your Main Character and who is your Influence Character. To give you an example I’m working on a story where the MC has an actual dark side - it manifests itself as a character. This dark side could have been the IC, but I thought it was too… “well, duh” as you said. As such another character is the IC, and the conflict with the MC’s dark side is kept to the MC throughline. But it still exists : it’s just that the storyforming and storytelling will be less in-your-face than “Stop rejecting yourself and you can achieve happiness.” (Which is what a Dramatica argument looks like : it tells you if the MC changes or not, what his problem / focus is, if he stops or starts something, if the story ends in success or failure, and if he feels good or miserable about it.)
You can do it however you wish. Are the MC and IC brothers / sisters ? Or do they have siblings and are themselves unrelated ?
You can write of the success found when two siblings stick side by side. You can write of the tragedy arising from betrayal. You can also make it bittersweet : maybe they fail at the overall story but are better off together ; or maybe the MC feels miserable for not having been by his sibling side before and now nothing, despite their success, will be the same between them.
And with that general feel, you can determine which perspective has which throughline : Universe, Physics, Psychology, Mind. If you want your MC to change by dropping a trait or remain steadfast, holding out for something to stop ; then you know the OS and MC will be horizontally aligned (Universe/ Activity, Mind / Psychology). And vice versa with Start (Universe / Psychology, Physics / Mind). The choice of throughlines will change how the argument is written and flavour the kind of conflict you have.
So an argument about sibling having each others’ back could be anything between “Start allowing people in your life and you can figure out how to work things out with your sibling” to “Everyone suffers the consequences of losing a loved one when you stop protecting what you hold dear.” The choice is yours