And Bremen and Kiel have such defences in any number?
The failure was not attributable to the pilots, they hit (with amazing accuracy given the technology of the day) what they were meant to hit, it was the brainiacs who planned the mission who got it wrong.
Do Schweinfurt and Regensburg not have these defenses?
The Oslo raid was postulated as an example of Mosquito's efficacy. A failed mission doesn't set a good example. As for poor planning, what would you have done to insure mission success? Crews were not sufficiently practiced in technique and time restraints prevented further honing of skills. It was a crapshoot and they lost this one.
Perhaps, if the British Air Ministry had insisted on developing the Mossie as a dive bomber....