Settings plus map conditions does not make an optimal SP opening.
Opening just Trad here would probably have your first 4 cities 2-3 pop higher, and the Observatories would probably be 8-10 turns quicker in getting up as a result. Not to mention being 3 policies ahead of where you're at in Rat. And you could've built just as many cities here whatever SP you open, given you're on Warlord. Maybe even if you don't found as many cities under pure Trad, but pure Trad founding equal numbers of cities is ahead.
Meanwhile opening just Liberty here, and you've got an extra Academy, you've improved your dirt earlier, and you're 4 policies ahead working on your 5th. After all, you don't need border expansion that much since you are Shoshone.
Heck even opening just Piety, you're probably in a similar spot with city count due to no pressure whatsoever, slightly smaller size, way better Gold/Culture/Faith production.
I'm not sure which leads to a faster VC under diplo, but I do know that on higher diff's it's not a hybrid. Going 6 cities then waiting until your 6th policy to get your first Happiness policy (Monarchy), leaves a LOT of Gold on the table. So you're essentailly carrying all of the Gold disadvantages of a Liberty opening with only a limited number of shared benefits. Unless of course you completed all CS quests, founded a Double-Building Religion w/o a Faith Pantheon, and essentially own everything outside your empire because you're on Warlord. That case, maybe just get more stuff, I don't know.