I think the US system is a lot more flexible than the European system, since it's a lot harder to create and organize a new party in Europe than to shift the direction of one of the US parties. The latter can be done one politician at a time.
Well, now, I wouldn't think that was true. It's easier to create a small boat than turn around an aircraft carrier. In Canada, which is arguably similar to Europe, parties start up, balloon up, and pop on a regular basis. Similarly, in Europe, I'd argue that it was easier to make the German Green Party or the Pirate Party an electoral success, at least enough to get its points heard in parliament and the press, than to turn the Democrats or Republicans into a Green Party or a Pirate Party. Think of the votes one of those big tent American parties would lose nationwide if they actually adopted a (for now) minority viewpoint. The urge to govern the nation squishes minority opinions, even when they are well-regarded and electable in one region.