"most people mean"

implies most people since the King James version was published. Not at all clear that's what author meant; the concept of the world as we now know it didn't exist then.

So very reasonable to conclude that the Great Flood in Genesis was meant to describe a regional megaflood, which innundated the "whole world" meaning all of Mesopotamian civilization.

And there is archeological evidence of ancient cities totally buried in mud, i.e. as you say regional megafloods.