You said it yourself, they "infiltrated and took down a warship". That's more spy action that this episode could boast. You also forgot that they infiltrated a whole assembly, fooled guards around, and had one of the girls taking great risks in the shadows to try and steal a prototype, before going a wild car chase in the city.
This episode it was just "morgue work, Dorothy with her father, "pay debts", dive in the past, cipher found, father killed".
A good anime episode, but a bad PriPri one.