Scaling triple secondary-mount problems to five inches

Would a 5-inch 38-caliber triple turret suffer the same problems as the British 4-inch Mark IX triple mounting?

Probably yes; the larger triple mount would still be difficult to aim and arm effectively.

The answer is a qualified yes. A 5-inch triple secondary mount would probably reproduce the difficulty of aiming and arming the British 4-inch Mark IX triple mounting. Increasing caliber does not remove the operational complications already exposed by a crowded multi-gun installation.