When was the last time the Republican nominee was arguably more left-leaning than the Democratic one

[Unconditional Surrender Truman]

Ford was probably more culturally liberal than Carter, the same might've also been true of Dewey compared to Truman.

In what sense? You seem to be equating cultural liberalism with being more upper class.

This is a pretty major undercurrent in the "party switch" narrative that bears addressing. Especially coming from the likes of Chernow, &c., a lot of it is just blatant classism and paternalistic disdain for poor white people in rural areas of the South and Midwest.

[Unconditional Surrender Truman]

1912 stands out.

There are WAY better arguments than this.  It literally entirely hinges on “Wilson is racist, racism is bad, racism is conservative.”

Not only was Wilson a prominent progressive, he was the essential figure in the evolution of modern American liberalism and a bridge between the ideology of the old Bourbon Democrats and what he called "new freedom." Calling him to the right of Taft is laughable.