The external GTA had a much larger territory to cover, and contrary to Sol, their forces were growing increasingly thinner after the DS-Sol node collapse, given that hostilities with the Shivans didn't end until a few months after, not to mention the HoL left to be dealt with.
In Sol, even if you don't have a single destroyer operational, you can still launch fighters from stations and be anywhere in the territory a few minutes notice. In the rest of the GTA territories, you need at least one base in every controlled system. Which is not exactly a given after years of war and tremendous losses.
Long story short, whatever the Sol/rest fleet ratio is, the rest of the GTA is spread much thinner and hence has potentially much less control over its territory than Sol forces. If anything, Sol should potentially be much stabler politically/militarily-wise than the rest of the GTA.
Not to mention that the whole civilian political leadership and infrastructure was most likely based in Sol. Which means, again, potentially more stability and smoother post-collapse transition.