just got back into the game after about 2 years and thought i would chime in.
EMP guardians plus sniper guardians=instant death. seriously, i was a good way through an 8/8 game and gave up after i realized this combo meant certain death. the only way i managed to counter it was by putting my fleet inside transports on a planet that i thought the ai would hit next, then unloading the transport right after the guardians showed up. i still lost the command station but the attacking force was dealt with. unfortunately, this didn't stop the ai from doing it again, and again. so, not wanting to deal with it i just gave up.