Willa Cather?

Homer, or the Homeric tradition, arose as rootless people displaced by drought and war in ~1,000 BC needed to sell the idea that entertaining stranger guests who had only stories from afar was worth doing, and that they shared common gods (versus the city-specific gods of earlier). This mind-set supported looser city-state alliances and cultures open to trading and ideas, who then outgrew the more xenophobic cities (like the Etruscans). So they semi-accidentally created a legitimizing belief system and thereby stumbled into founder roles.

America as the land of opportunity has flourished by acquiring more land and capturing value better, mainly by diminishing obligations to country and god and fellow humans. Yes, many writers bore witness to the frictions this involved with varying degrees of acuity or tragi-comedy, but no American writer wrote in a way that actually established this American mindset.

I think instead the mindset is perpetuated by each era building achievement heroes, stimulating belief in unbounded personal possibility. American literature is reduced to pointing out the vacuous consequences. As William Carlos-Williams wrote looking into his mirror in middle age, "I am lonely, lonely. I was born to be lonely, I am best so! [...] Who shall say I am not the happy genius of my household?"

If I had a vote, I'd nominate Willa Cather as the writer who portrayed that knowing moment of the powerless, non-achieving people enthralled with the beauty of nature as it was being destroyed. It's not what guides Americans prospectively, but it might best reflect history's perspective and our own retrospectives.

(I should add that I'm glad America has hoisted individuals and done so much to lift the global standards of living and care, even if it was more by greed and necessity than charity.)