How British sloops used the gunboat exemption

Could the gunboat exemption be stretched into a genuinely useful warship?

Yes. Britain used sloops with twin 4-inch guns for minesweeping, minelaying, and anti-submarine escort, freeing destroyers for other tasks.

British sloops gave the gunboat exemption a practical naval use. Twin 4-inch guns were considered more useful than a 6-inch weapon on a vessel of this size. The resulting ship could sweep mines, lay mines, and escort against submarines. Assigning those duties to sloops released destroyers for other work.