So, post 10,000 could go to defending Marina. Hell, why not?
You're leaving out something quite significant. Everything that she didn't do, in my view, is balanced by her importance to Setsuna's development as a character. There is more to his growth than just achieving innovation. That evolution was accompanied by a dramatic shift in his thinking. Original Setsuna was just fixated on fighting to make things better. New Setsuna, unlike Ribbons, became focused on the need for understanding and the need to change himself -- something Ribbons would never consider. It's even a massive change from the start of the season, where Setsuna tells Marina that he can't think of a way to live besides fighting. Marina put the idea in his head that he should strive for something more, and Saji was a physical reminder of the distortions Celestial Being and himself helped create that he needed to help fix. We also see this in the example of Graham/Mr. Bushido.
I also think that Marina, while easy to mock for her reticence, is pretty clearly representative of the fact that there are people in this world that need to be fought for and protected because they lack the means or power to fight for themselves. For much of the season A-Laws was taking actions against targets it clearly outclassed, and information control meant that almost no one was hearing about it. And frankly, even if Marina had joined Katharon, it wouldn't have made a difference without other factors intervening. Katharon had to take advantage of events that happened outside of its control.
00's world, much like our own, can be at times be very kind--and very merciless. The truth is that not everybody can make like Picard and turn on the charisma and provoke massive change. Especially when no one is listening! One could compare Marina unfavorably to her counterparts in other timelines, but the simple truth of it is that Marina was dealt the worst possible hand by way of comparison. Tyranny had the upper hand by far in season 2, hence the need for the Gundams to step in and even the scales.