The Shoshone get what they want from ruins, but ruins aren't generally too bad, randomly. Even when I get a map, if I get it early, it often shows me another ruin or two. If I get two bad ruins in a game, I generally consider myself really unlucky. They also get their second Pathfinder out more slowly than anyone else gets the first scout. While the first obviously has a scouting advantage over a warrior, to what extent is a roll of the dice (if you find yourself close to a desert, no so much).
I'd probably rather roll with America, in general, for scouting. You can see more, and therefore get more tries for good things, as well as being more likely to hit a few more CS's first.
Admitted, I haven't played with them, but extra land is really something for early game, and even then, it won't generally be a massive deal. More land sooner in a game means little unless you can use the advantage. Using tiles in the second ring right away generally won't make a big difference. Getting them in the third sooner could be somewhat more rewarding, but either way, it's an advantage that dies off.
I'd rather have Ethiopia or...almost anyone that has an early building that can easily be put in cities, which gives a slower start but keeps giving.
It just seems that the Shoshone have to win early or fight and claw late. They have 2 UU's, one only nice while warriors are relevant but also expensive to build compared to the normal unit, and the other a minor upgrade to a unit that you probably won't use in great numbers. The UA could be anywhere from great to mediocre, depending on how resources fall (and land around them), but in the end, they don't do anything so amazing.
They don't have ranged knights (or pikemen, even). They don't get faith from the first building they can make. They don't end up with more gold, culture, faith, etc. than anyone else.
They are the reverse of America, the ultra standard civ that only gets bonuses that aren't really very simple to exploit. America just has to survive early and get the UU's late, while seeing the whole world. The Shoshone have to ride their early advantages to the end of the game.