Why a peer-war fleet still needs a flagship

Does a navy still need a dedicated fleet flagship when such ships spend much of peacetime in port?

Yes: peer war demands mobile, survivable command capacity, extensive staff space, sensors, communications, and processing that ordinary escorts and carriers cannot spare.

The case for a dedicated flagship begins with the staff and equipment needed to coordinate air, missile, surface, submarine, drone, electronic, and ballistic threats. Adding a large command staff to a destroyer would require accommodation and workspaces that the ship was never designed to provide. A carrier offers more space, but its equipment and operating position also have to serve its air group. Shore headquarters depend on communications reaching the fleet, so their suitability cannot be assumed if satellite links are disrupted. A separate command ship would let the fleet commander move without taking a carrier or another valuable combat unit away from its own task. Historical flagship choices and the proposed ship's potential relief duties develop these arguments further.