Why a serious amphibious ship grows so large

Is there a size at which an LPD or LHD becomes useless, or too large?

Below about 8,000 tons modern capability becomes limited, while large powers can use 40,000- to 50,000-ton ships; size is driven by the equipment and force level required.

The answer argues that a ship below roughly 8,000 tons has limited room for modern capability, while first-rate powers may use platforms in the 40,000- to 50,000-ton range. Tank weight and the growing amount of equipment to be carried explain much of the expansion; the right size follows the task and desired force level. Mid-tier capabilities cluster lower because they trade aircraft, vehicles, command space, endurance, or protection against cost. The useful lesson is that displacement is an outcome of the force package and operating environment, not a universal measure of quality.