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Mumford and Sons make the same song over and over. by R2D2isAMeanDrunk
It's a successful strategy in pop music (see: Foo Fighters, Green Day), but it doesn't win a lot of hearts and minds if you don't have the back catalog. I think Of Monsters and Men is pretty close to Mumford and Sons but maybe with a little more range and less reliance on the banjo.
Full disclosure, I've got a soft spot for any really talented female singer, and Florence Welch of Florence and the Machine has tremendous talent and seems to enjoy experimenting in very different compositions, if not genres. If you've only heard Dog Days Are Over from her, I wouldn't blame you for lumping into the same faux old timey music as Mumford and Sons, but she's got a lot more diversity as evidenced by newer singles.
Edit to add that Edward Sharpe and the Magnetic Zeroes definitely fit in that category but they're a band that knows what they want to be and that happens to be what they are. That's their comfort zone and they're going to just keep making music there. I give Lana Del Rey credit for this too - she knows what she wants to be, it's different than most of what we hear, and she seems to be working to get better at it. She fails more than she succeeds in creating great music, but I'm just happy to see people trying new things.