And those 4.5 fighters will still kick your ass. If you want to compare apples to apples (bonus ship vs bonus ship) the bulletproof fighter has 2x the health and speed in return for 80% of the base dps of the zombard (and 3x the bonus dps)
Bombers, zombards counters, have both a higher dps and a higher bonus then the zombards.
So you break the initial volley with your frigates. If you haven't managed to anger more then then equivalent of 7.5 times the size of your frigate fleet, they will survive the barrage. If they don't, so what? You just ate half a minutes worth of a force over 7.5 times your size, 30 seconds is the equivilant of a EMP. Send in your bombers and rest of fleet, and watch the bombers alone dish out damage three times as fast cap wise then those bombards.
Zombards are only hard if you either get yourself into a strategic black hole in which case a single EMP or raiding[baiting] elsewhere can dig you out of such a bad decision. They are very frail, very prone to overkill, slow, and have poor bonus dps.