so basically, i looked at four works: beowulf, myths and romances of the middle ages (which contains the first 'retelling' as opposed to just a translation of beowulf), grendel (probably the most famous retelling), and the mere wife (probably the most recent retelling) and looked at how perspective shifts: the first two are in third person, the third is in first person, and the fourth switches between several first person and first person plural narratives
they also move from having the most clearly delineated monsters and heroes to the least clearly delineated monsters and heroes
so it's along those lines. it's nothing new: other researchers have noticed that readers tend to question what's going on in a story more when it's in first person (think, e.g., unreliable narrator), so that tends to gray things out more.
myths tend to be told in third person because they have very specific perspectives: a lesson to be taught about history or how to act.
thus you get this trend from a third person, morally black and white story in beowulf to a morally gray story by the fourth retelling, which is in a primarily first person form.
here's another example about how perspective affects things: it makes 'bad' characters more bearable if it's in first person. think of humbert humbert in lolita.
so grendel, the third retelling i looked at, kind of takes this approach: it makes grendel seem okay because it portrays mankind as equally evil.
there's this one really pointed line where the scyldings call the government 'monstrous' as grendel is off to the side listening in - might as well wave a giant sign saying, look, look! the monster isn't the only monster!
the mere wife is really interesting inasmuch as it doesn't portray everyone as equally evil, but as equally good, in a way.
feel free to ask me questions about it - sorry for the text wall.