An objection to large interwar sloop orders is that ships built early in the decade might be obsolete by 1939. Their core requirement was to carry ASDIC at modest speed, so that part of the design would remain useful. Sufficient electrical power would also allow radar to be added when it became available. The Black Swan comparison presents these ships as capable, purpose-built submarine hunters rather than disposable substitutes for wartime corvettes and frigates.
Notable Point · 1:29:51-1:31:00
Why interwar sloops could still take wartime sensors
An early-built sloop would not become useless before 1939 because its slow escort role left room to add ASDIC and radar.