Trying to usurp power over a minor faction via bribing their ruling 'whatever' could result in the minor faction wanting to call in the other major player to help maintain their sovereignty from would-be aggressors trying to steal their freedom. Because even though these days 'we' might be used to ultra-corrupt and degenerate people in some countries leadership being puppeteered by money oligarchs, the oligarchs that do the puppeteering and the drama those officials play, is one thing, the rest is the actual people, who have sneakily power taken away from them by an outside power. So in such a case, of a betrayal of their so-called elites, the people in order to restore their sovereignty-power, are inclined to call help from outside powers to remove an usurper vassal regime that would of course try to use all means of oppression to cement its hold, on outsiders behalf, all the while utilizing the official language of love and freedom, that just happens to be the opposite of reality and what they want to remove. Also, assault on indigenous culture, subversion, trying to inspire drug use in order to bring down a society. History is full of examples of that. (opium wars etc)
more practical suggestions:
Minor factions, having good relations with them, could somehow grant you the ability to build special items/slots either on ships, or special buildings, even defense turrets, ships. (something like you can do with pirates on asteroids as tec rebels T3)
Are directional shields still planned ? Like the shield on the old game Starbase that had frontal deflector shield. A minor faction could either give access to that to be built, or your cap ships would gain the ability to have that special kind of equipment in minor faction grav well.
when it comes to items for cap ships, there should be differences between loyal and reb factions. Since divisions took place, they no longer are the same factions, the philosophy of their defense/war strategy dictates the equipment,(not demagogues) so aggressive vs heavily defensive outlook will inevitably produce different things.
In Rebellion you had each faction with own particular corvettes that could pretty significantly alter the gameplay.
Like Vasari has an overgrown fighter Defensor doing PD and general light firepower, there is space for a missile corvette too. instead of a bomber.
TEC fighter is called interceptor. Using WW2+ terminology, Interceptor was the thing to get the heavy bombers. Ability to go high fast, at the cost of dogfighting ability. Later on, Interceptors in some countries became long range patrol planes. Normally outside the reach and performance of a front-line fighter. Those normal fighters service ceiling IRL is about 16km. (F-16, MiG-29) Interceptors, say MiG-25PD was able to go higher, faster, later iterations, like 31, quite modern planes, became carriers of heavy 'very fast projectiles'. But IRL the planes are huge. The ... 'interceptor', could work similar to a corvette, but also a sort of like cavalry archer, where it just keeps sending the missiles while keeping distance. Its missiles however should be able to target fighters or bombers. Otherwise it would be just be some reskin of Javelis with weaker missiles, perhaps something like bombers. (80/20 per missile 120 pen, something more than 20 pen of fighters) Anyway, Im getting into too much detail, which might not be actually useful.
So, there could be carriers, or items that could provide some squadron/s of interceptors, that do use missiles against their targets, primarily bombers, from range. Missiles could be faster than usual, so light corvettes like scouts would be unable to outrun them.
Again, properly used proportional navigation should work fine as long as the missile is faster than the target.
So, that would add some more missile saturation, more missiles to saturate PD with perhaps. Interceptor as a super-heavy fighter anti-fighter/bomber.
It is very far from making an 'integrated space defense' though
I think some of the ideas are actually pretty cool )