The exo-waves are really meant to crush forcefields, honestly; the force fields are pretty much paper when the spirecraft are around. And actually if you have 50-100 bombers sitting outside a forcefield, it should be down in seconds. Otherwise, forcefields are basically just "perfect invincibility except in extremely unlikely circumstances that don't even occur in every game." Though if you're playing fallen spire, you'll obviously see that waaay more.