This was one of the war's most important lessons: without artillery support (whether naval or CAS), paras get minced by dug-in defenders, due to their lightweight nature. An enemy who knows in advance where the landings will occur (and deploy 3xA) can turn a drop into a one-sided bloodbath.
Pretty much the only role in which paras were of any real use was night HALO drops for sabotage and/or forward recce and/or specific target designation/'painting'.