Type 91's magazine and crewing distinguish it from an arsenal ship

Is the Type 91 uncrewed missile vessel essentially an arsenal ship?

No; its smaller magazine and absence of even a lean onboard crew make missile sloop or missile barge a more accurate description.

The arsenal-ship concept discussed here combines hundreds of missiles, a very small crew, and little independent sensing. Other ships provide the information and direction needed to use that magazine. The Type 91 proposal carries too few missiles to fit that description and has no routine onboard crew. Missile ship, missile barge, or missile sloop are therefore the preferred descriptions in this exchange.