Personally, I think Rarity could've used some more to her backstory. She's a perfectionist, decorated a boulder, got a crowd's attention, Cutie Mark. End of discussion. But I think Pinkie Pie and Fluttershy are fine, because Pinkie was talking about how she was different from her family, like how she was bright pink, and then Fluttershy told how she was bad at flying and was made fun of. But, in general, I liked all the backstories