Seconded! OP, in a similar vein as the world building games you already mentioned, you might find Intrepid interesting. I could see it being used to do world building + history of some of the major players and nations therein.

I could also imagine the relationship map it uses being hacked a bit to allow for some Disco Elysium style personality skills / thought cabinet shenanigans if you were interested in leaning into that in particular.

Thank you, I've realised that my approach seems a little different from other here, where I try to pick an RPG for an idea that's forming in my head, based on the genre and tone, settling on an RPG that's 80% there but people love the ruleset, then I chop and change it to get close enough to 100%.

This is probably detrimental in a few ways too, as some games like Lancer are unchangable until I'm familiar enough to peel apart the interwoven mechanics and lore, and I'm not going to touch it because I almost never run official settings and adventures, particularly in longform games.

I will shout out both Alice is Missing and For the Queen, which both get worse when they get altered, because their strength comes from their simplicity and then probably ridiculous amount of playtesting.