Was the flood described that took place in Noah’s day reduced in severity by divine intervention to help preserve humanity?

This is very much the case. We were able to reduce and thwart a number of the calamitous so-called natural disasters they created to inflict punishment and destruction on human civilization. This could have annihilated humanity altogether and is the reason the stories persist from those prehistorical ancient times all the way to the present because the events themselves were supernatural in forcefulness and all but overwhelmingly lethal in their effect on humans of the day. It was through a divine rescue that enough were spared to keep humanity going and allow a recovery.