First Deity Victory
Man, I remembered when I came here, I was stuck on Emperor. Well, I kept playing and climbing, and then I got to a point where I was winning Immortal even with crappy leaders and bad starts. So I decided to try Deity.
Compared to Immortal, Deity is a quantum leap. The AI expands/techs/builds so much faster, and you have to fight just to get the land you need. I had many games where the initial REX/rush just didn't work, then sometimes I went hopelessly bankrupt, then other games with the opposite problem (suffocated by the AI).
Well, I kept trying. And then in a recent game, I realized we had some factors necessary for a Cultural win (a solid GP Farm and a good diplomatic environment, albeit the land wasn't great for Cottaging.)
So I played for it. I probably would have taken longer, BUT some time in the mid-1400s, one of my cities managed to flip Sitting Bull's CAPITAL. And it had already had all these wonderfully Cottaged land and Cathedrals, even if Sitting Bull wasn't using them.
And we won in 1852! Thanks to everyone else for the advice they've given me over these months and years!