I don't reject the strategy. I think it's a fine one. I just think there are serious challenges to it that aren't yet addressed.
Indeed. A good way to enhance it would be to distract the League from this approach.
I believe that a series of raids deep inside the core worlds of the league could work finely in that direction. Just go to some wealthy or well-known system, wreck a few space installations, grab a few merchant ships and or just parade around it for a few days. It would require a certain number of warships, but in fact not an unreasonable one, and not for that long, because you just need to make a few apparitions here and there in order to mark the core systems (the one that count).
On a purely strategic or militarily point of view, those raids would not represent any sort of real threat, but since the SL government is totally corrupt and deeply in the pockets of many interstellar company, their CEO may feel directly threatened, and call for an increase of the defense of those core systems (depriving, of course, the rest of the league and the protectorate). This, coupled from the pressure coming from the citizen and governments from those system may well force them to divert a lot of forces to places where they are in fact not really needed (or useful). And thus preventing the SL from either stopping the GA from liberating other protectorate, or coming back to retake them when the GA leaves.
In fact, if those raids are made in a really spectacular way, the liberation of the protectorate may fade so much in the background that it would be nearly invisible to most people, and just look like a minor inconvenience.
So, in short, make them so much afraid of the guy knocking at the front door, even if he cannot enter, that they would not notice the other one destroying all the trees in the garden behind (and thus leading you to starvation.
This sort of strategy would lead to the fixation of a lot of the SLN, the dispersion of those forces (all core systems will want some form of protection) and remember that the one that protects everything protects nothing. With the dispersion, those forces could face defeat in detail (it would require a higher number of ships than the first raids, but due to the tech advantage, it could still be done).
I see a lot of advantage in following this strategy, because it would force the SL government to react most forcefully to the wrong threat. Only a government with a very powerful will and a strong position could do the right thing (not react to the raids, but to the protectorate erosion and launch deep penetration raids of its own). I’m not sure that all the Mandarins are smart or ready enough to affirm their will to do it. They for sure are not united enough for that. And I’m not sure they’re position is strong enough even if they should try to do it.