Why shipboard drone defense favors missiles and expendable interceptors

Could Fire Scout and Comanche features be combined into small containerized helicopters for persistent ship defense?

Not at the proposed scale; sensors and control systems keep a capable aircraft large, while expendable interceptors fit the mission better.

Combining Fire Scout's compactness with Comanche-like combat capability would require a substantial sacrifice in payload. Removing the pilot does not remove the sensors, computers, cooling systems, and electrical demand of a capable modern aircraft. An uncrewed aircraft also needs the command systems and communications required to replace decisions a pilot would make locally. It must either carry sufficient processing power to react onboard or transmit enough information for a control station to make those decisions and return new commands. Those requirements limit how far the proposed helicopter can shrink. Expendable vertical-takeoff interceptors are a more plausible option for ships with little aviation space because they can be stored inside and brought to an open area for launch. The alternative is a small number of larger and more capable systems, with the associated cost and support requirements.