Humans have the sturdiness/hardyness of cockroaches. An individual human or an individual human ship is easily bitch-slapped. It's just that the humans keep coming over the corpses of their dead, and they keep adapting to the pesticides used against them.
This is NOT toughness. Toughness requires for the individual human or ship to be hard to bitch-slap, to be able to take a lot of damage before succumbing.