Why Type 31 resembles a modern sloop

Is a Type 31-sized general-purpose ship better understood as a sloop than a frigate?

He thinks the older sloop label better captures a general-purpose ship with anti-submarine and amphibious capability.

The historical sloop was a general-purpose vessel with anti-submarine and amphibious utility, not merely a smaller frigate. That makes the term a better conceptual fit for Type 31 than a label driven by present-day naming habits. Possible Type 32 differences remained uncertain, so the available announcements did not support a firm conclusion.