There's also a huge damping variable due to communication latency between star systems, and of course travel time if you want two armadas to gang up on a third system. In fact this is exactly the two generals problem: you really don't want to launch an armada without confirmation from your ally, and if you do launch it, you will have the two generals problem recalling it.
https://en.wikipedia.org/wiki/Two_Generals%27_Problem