Are you sure? Both sides use the same combat rules. Are you talking about what you see or have you checked the combat log too. The thing is every turn all ships of one side are trying to kill one single ship on the other side (i think the one with the highest attack). If they finish it, they start to kill exactly one other ship. Hovewer the cinematics may look like different. Beam weapons fire very fast, torpedoes and rockets are flying some time. But for the game mechanics it is not important. Destroyed ship does not fire anymore even if the torpedo, that killed the ship is still on the way (cinematics).

You can find the exact mechanism here https://www.galciv.wikia.com/wiki/Ship_combat

Then the combat viewer UI has long needed a makeover {grin}, at least down in the bottom where you see the "damage floods" on the individual ship icons.