Why early helicopters were poor ASW substitutes

Could early helicopters or autogyros have replaced fixed-wing aircraft in anti-submarine patrols?

Not effectively; they lacked the endurance, sensors, reliability, and search coverage that made the Swordfish useful.

Carrying a light depth charge was not enough to make an effective ASW helicopter. Without mature engines and dipping sonar, a helicopter offered less search coverage and loiter value than a Swordfish carrying radar, depth charges, and later rockets. Early power-to-weight ratios also limited fuel, endurance, reliability, and useful payload. The comparison makes sensors and time on station as important as the mere ability to hover.