Did sloops score more U-boat kills per hull because they were better ships or because of how they were used?
Short answer
Both: their capabilities mattered, and they worked in high-threat areas and hunter-killer groups where they had more chances to engage submarines.
Notes
The sloops' higher U-boat kill rate per hull reflected both design and employment. They were sent into demanding anti-submarine areas and frequently assigned to hunter-killer groups. Their greater speed than many frigates helped them pursue contacts beyond close convoy escort. Assignment patterns mattered alongside differences in equipment.