It appears there are a lot of advancements to come yet. These Interceptors alone are adapting and Posing an issue as it is. In the beginning I don't remember them using that scramble pulse they do now, so their weapons alone are developing.
It makes sense that even if they are supposably retreating, they are headed into enemy territory (being us, a 100+ year old threat) And will be sending out weaker individuals as probes to seek and find weakness. This explains why we have not seen any of the smaller 'Scout' Class Ships yet. it would be illogical to send units knowingly forward with a high probability of failure. When they arrive they will more than likely travel in pairs to increase odds of survival.
As for the 'Mothership' if we can call it that, it would have to be huge to accommodate for all the Interceptor ships alone. In fact there would be numerous 'motherships' with massive size and scale. (the base Concept suggested before makes a little more sense in terms of resources) but, it is very probable there are larger, Militarised Destroyers or Thargoid Capitol and Dreadnaught ships. Motherships would be bigger than the 3 combined....
Many possibilities lay ahead, Their weapons, ships and size are always a surprise to us. Best we be careful what we wish for though...
CMDR Jaylem