River, Loch, and Bay frigates followed yard and convoy needs, not destroyer treaties

Would River-, Loch-, and Bay-class frigates grow in a world of much larger destroyers?

Probably not by much, because their size came from yard capacity, construction standards, and mass convoy-ASW requirements rather than destroyer limits.

River-, Loch-, and Bay-class frigates were not scaled directly from treaty destroyers. Their dimensions reflected what a wide range of yards could build, often using practices closer to commercial construction than those of a fleet destroyer. They were intended to provide mass anti-submarine coverage for convoys and amphibious groups rather than to fight as primary fleet combatants. Larger destroyers might change sloops or high-end escorts, but not the basic economic logic of these frigates. These were mobilization vessels rather than ships optimized for the battle fleet.