How does the Main Character Problem work within Steadfast Characters?
As I understand it, the MC Problem is what's "wrong" with the MC.
In a story where the hero Changes and the outcome is Success/Good, this is the character flaw the MC has to overcome in order to solve the story problem. In a story where the hero is Steadfast and the outcome is Success/Good, this is what everybody else thinks the MC is doing wrong. In reality the MC Problem is what allowed him to overcome the story problem. (For example, I think Dirty Harry or Jack Bauer's MC Problem could be that they're willing to break the rules to get results.)
Is this right?
Not quite. You've confused a few different story points.
Success is tied to the Story Outcome and determines whether or not the story goal has been achieved.
Good has to do with the Story Judgment and is related to whether or not the story inequity was resolved, as opposed to the MC Problem.
Change has to do with the Main Character Resolve and indicates that the MC has adopted the MC Solution.
Each of these are independent, which means you can have any combination of Outcome, Judgment,and MC Resolve. The audience may infer connections between these because each has part of the meaning in the story, but the CAUSALITY is non-obvious and non-linear.
For Steadfast MCs, it's best to think of the MC Problem as the source of the MC's drive. What other characters think it is may not be relevant and is not relevant to its functionality in the story development.