What actually IS good against them? They are getting to be a nuisance as the AI is deploying them in large numbers; they don't do a whole lot of damage until you've killed most of them, but they have silly amounts of hit points and nothing seems to kill them quickly. My giant strike force of tech I-III space planes that instant-vaporizes any other tech II unit that enters its range takes multiple volleys PER Z Elec Bomber...
It has actually become a running gag with my ally "Oh, hey, we got a new unit. ...Guess what? It's Weak Vs: Z Elec Bombers..." One thing I notice is that as you tier up ships actually get ~worse~ against them?! Tech 1 fighters are Strong Vs. them, but Tech III fighters are badly Weak Vs. them, which seems very strange. Also all three of fighters, bombers, and frigates are listed as weak against them at tech III... Space planes are not very good against them, neither are teleporting battle stations, or chameleons, or MLRS...
We can kill them eventually, of course, it's just that the AI is habitually fielding 50 per planet now on almost every planet, so it would be nice to know if there is a trick to killing them quickly...