As a sample here's the makeup of convoy PQ-17 which was carrying the most valuable cargo ($700 mm) to date in the war by the time it sailied in June/July of 1942:
33 merchant ships plus 1 oiler to refuel the escorts - 3 rescue ships
- 5 destroyers
- 3 corvettes
- 3 minesweepers
- 4 anti-submarine trawlers
- 2 anti-aircraft ships
- 2 submarines
25 of the merchants were sunk.
So yes, the number of destroyers are historically correct. You're not paid to sink warship tonnage, you're paid to sink merchants! Go get 'em! 