I need help understanding Royal Navy WW2 sub hunting doctrine - doesn't the plan of using fleet carriers to sub hunt (with or without escorts) seem like a very high risk, low reward scenario?

IIRC the RN took fleet carriers off of sub-hunting duty after HMS Courageous was sunk on September 17, 1939. Ark Royal was not sub-hunting when sunk, was ferrying aircraft to Malta. RN also lost HMS Eagle to Uboats during a Malta operation (PEDESTAL). Surface vessels were always at risk to Uboats in the Med, as the various islands and straits create choke points where it's much easier for a sub to get lucky than in the North Atlantic.