The statement about the OG Civs being "boring" is only part true. Compare Germany and Japan to Persia or the Iroquis. Both of the latter have highly interesting abilities and units/buildings. There are just a few very painful offenders in Vanilla, but most of them still have nice tricks that wouldn't go amiss on new civs. Heck, Poland is bland as can be (Let's be honest here, they ARE!) but that doesn't make Poland weak either. Of the generally considered top tier civs (pre-BNW; Inca/Maya/Babylon/China/Korea), sure, only one of them is from Vanilla. Still doesn't mean they're all poor.
Now on to the Shoshone. The thing about them is that while powerful, their entire bonus focusses on the early game. They can set up a fast culture/faith game, sure. Or troll their closest neighbor with Comp Bows in the ancient era. But on the flipside, once other civs stabilize, they tend to get bonuses...which the Shoshone don't. The Comanche Rider, while not a POOR UU by any means, is just not special enough like, say, the Keshik to be able to carry the Shoshone further.
Their combat bonus is like a fixed version of Ethiopia's, which is annoying but nothing spectacular. Still won't save them from some artillery fire.
Now, if they get that huge territory + tradition + Great Wall going on...then you're in for a long slog. But they don't offer any other bonuses that helps them actually win the game - they simply have a much smoother early game then most others.