Why wartime carriers did not need angled decks

Would angled flight decks have given wartime Royal Navy carriers a major advantage?

Not much; the angled deck became necessary mainly because jet landing speeds made straight-deck bolters and overruns much more dangerous.

Low-powered propeller aircraft could land and take off on different portions of a straight deck. A barrier separated the landing area from aircraft parked ahead. Faster jets were more likely to overrun the arresting area and strike those parked aircraft. The angled deck therefore became a much more important safety and operating innovation after the war.