Since this I tried doing a full copy of the /boot and /game folders from someone who has the game working (in case a clean install didn't work somehow) and still had the same issue. Ran dxdiag and sfc scan, neither came back with issues. One of the first things I tried for this failure was updating my graphics drivers (to 475.06), but several people had it work to roll those drivers back (474.82). No luck for me. I double checked to make sure my GPU was not overclocked (it wasn't and isn't).
Next steps are to try a different GPU and/or I'm about one cup of coffee of motivation away from reinstalling Windows 10 + FFXIV from scratch on my other drive and trying over there.