Heck, even I don't claim that these Genesis stories that are expansions of Sumerian legend are "just plagiarism".
Can you really cite anyone who maintains that position? I would think virtually anyone who thinks the Bible used Sumerian texts is also willing to believe that the text was modified and edited here and there.
I wonder if you have over-stated the problem with Panbabylonism ...
Wikipedia has a very short blurb on it:
"Panbabylonism is the school of thought that considered the cultures and religions of the Middle East and civilization in general to be ultimately derived from Babylonian myths which in turn they viewed as being based on Babylonian astronomy, often in hidden ways."
Perhaps you are confusing PanBabylonism with the "Bible-Babel School" ? ? ?
"A related school of thought is the Bible-Babel school, which regarded the Hebrew Bible and Judaism to be directly derived from Mesopotamian (Babylonian) mythology; both are forms of hyperdiffusionism in archaeology."
"Both theories were popular in Germany, and the height of Panbabylonism was from the late 19th century to World War I. Panbabylonist thought largely disappeared from legitimate scholarship after the death of one of its greatest proponents, Hugo Winckler, according to one author...."