I started VP recently and only play random leaders. Shoshone is the worst nation I've seen thusfar, and the first that I've genuinely been confused as to the intent behind, minus "not diplomacy."
The UA is just kind of mediocre. It lets you take less lucrative but more defensible positions and get better yields out of them early, and it lets you zone your neighbors - both useful but way more niche than other civs' abilities. The defensive combat bonus is a nice little boost, but if you're in a position where it makes or breaks the game, I'd argue you've already lost and you just don't know it yet. Finally, despite granting you control over ruin RNG, ruins even appearing are still at the mercy of the RNG and AI. Plus the fact that the ruin ability is really more about selecting the order of bonuses you'll get, not which bonus you get. Obviously picking a tech every time would be broken, as would rushing an Explorer (or even further), but I'm not convinced the other options - yes, even population - would be game-breaking given what the other civs can do.
The UI is fun - encampment "pillboxes" across the plains is neat, but the yields can make some otherwise terrible tiles very appealing... for a little while. They don't have nearly enough staying power unless you're going for a culture victory.
And then there's the real stinker, the Commanche. These poor guys show up way too late to contribute to or counter a domination strategy, and in their own way are a little microcosm of Shoshone mediocrity. They suffer the same problems as all cavalry: anything but a smooth surface and they grind to a halt just to be wrecked by the ranged units they're theoretically supposed to counter. Their only reliable use-case is a defensive war near the Shoshone's capitol, thanks to their plains preference.
They're also spread thinner than usual at the worst possible time to be spread thinner than usual: Ancient. You need to be cranking out settlers to zone off your opponents and later provoke defensive war. You also need to be cranking out Workers to get those encampments up so you can effectively defend against Ancient rush civs, but also be cranking out military to escort Settlers and provide ZOC on those encampments. That's a lot of production to ask from a Plains bias, and you still need to pray you find enough ruins to drive your Faith, Culture, Science, Gold, and arguably even Population (Settler Stagnation stings a little worse when you have all those tiles available) since you won't be getting infrastructure anytime soon.
idk, they seem genuinely terrible with one of the most tedious routes to victory I've seen yet.