Why American and British warship designs resist easy sharing

What would a Royal Navy version of the Arleigh Burke class look like?

It would diverge sharply in crewing, sensors, weapons, automation, and hull form, undermining most of the hoped-for commonality.

A Type 45 operates with roughly 190 people against about 330 in a Flight IIA Arleigh Burke, so adopting the American hull would impose a large fleet-wide personnel bill. Across six ships, the extra crews and the training and shore establishment behind them would consume well over a thousand additional posts. British demands for different sensors, missiles, automation, and operational endurance would further erode commonality. The result would reproduce the compromises seen in the Horizon frigate project rather than deliver a simple shared destroyer.