...I'm having some trouble following your argument, so I'll explain my understanding of the relationships between the Catalyst and the Inhibitor and move on from there.
If the MC Resolve is Change, then the OS Inhibitor is in the Domain Dynamic to the OS Catalyst. Also, the OS Catalyst is Dynamic to the RS Inhibitor, and vice versa. (So for example, if the OS Catalyst is in Universe, then the OS Inhibitor is in Mind. If the OS Catalyst is Security, then the RS Inhibitor is Threat. The RS Catalyst is Confidence, and the OS Inhibitor is Worry.)
If the MC Resolve is Steadfast, then the OS Inhibitor is in the Domain Companion to the OS Catalyst. (That is, it's in the same row.) Whichever character is in that domain (Main Character in Stop stories, Influence Character in Start stories), their Critical Flaw is Companion to the OS Catalyst, and their Unique Ability is Companion to the OS Inhibitor. (So if the OS Catalyst is in Universe, then the OS Inhibitor is Activity. In a Stop story, if the OS Catalyst is Security, then the MC Critical Flaw is Fact. The MC Unique Ability is Skill, and the OS Inhibitor is Wisdom.)
Why does this relationship exist? Good question. It's probably better suited for Chris and/or Melanie to answer, because they know all the little in-and-out reasons better than I do, obviously. That being said, it's clear that a Change MC is very closely tied to that motion from one state of being to another, which suggests to me the Dynamic relationship. As to Steadfast, this Companion relationship pops up in multiple places with the Steadfast Resolve, most clearly with the Critical Element, which is always Companion to the Problem element for a Steadfast MC. (For example, if the MC's Domain is Psychology, and their Problem is Unending, then their Critical Element is always Hunch, regardless of their Growth, Stop or Start.)
But your question is, what does the Domain of the Inhibitor/Critical Flaw have to do with the Domain of the Catalyst/Unique Ability? I'm not sure, to be honest. In a Change story, since the two Domains are Dynamic to each other, that means one is external, and the other is internal. That means their external desires/capacities are being thwarted by their internal desires/capacities, or vice versa. In a Steadfast story, the two Domains are Companion, which means one is static, while the other is dynamic. So the characters static beliefs/thoughts are being thwarted by their internal beliefs/thoughts, or vice versa.
I'm throwing this all together on the fly, but I hope it helps!