Category A procedures are based on trying to achieve a level of safety that is predicated on engine failure probability. Currently the expected failure rate of an engine is once every 10,000 hours. So for Part 29 helicopters (and those Part 27 machines that decide to use Category A), something has to be done to ensure the level of safety is met. Body counts of more than 9 get civil aviation authority leaders (ministers, administrators, etc) in hot water, so the end result is the Category A procedure.
It does not address everything, and someone said, no procedure can.
The Category A procedures in the FM are tested and proven by the company and the certification authority in the country of certification. In some places, the certification authority in the country of use will verify them. They are generally conservative and give margin for error and abuse. The procedures must be read in conjunction with the appropriate limitations of the supplement / section of the FM. If it says there is a size limit on the helipad, then that's a limit.
Have an accident doing a Category A procedure to a helipad that is smaller than the minimum, and you have just invalidated your Cof A and your insurance.
As for the backward takeoff - has anyone looked at the Bell Helicopter sideways slide technique? Easy to use, little loss of performance and very repeatable. Also much easier on the passengers...