^ actually the ship had "standard phasers," they were "fast but not giants." And the Enterprise, which withstood several passes of the vessel, only needed one connecting shot to cripple them and render their suicide mission moot.
It's like getting attacked by a ship more powerful and faster than the Enterprise with standard phasers but the ship didn't have any power left over for defense
SPOCK: The thing that confused me was the power utilisation curve. It made them seem more powerful than a starship or anything known to us. That ship was constructed for a suicide mission. Since they never intended to return to their home base, they could use one hundred percent power on their attacks.
I wonder if that suicide ship was just on the edge of blowing up in order to maintain the power output for each of those attack runs.
EDIT: Corporal Captain beat me to it