Apart from Pinkie and Twilight, the only member of the mane case who isn't guilty is Applejack. This makes perfect sense, because she is the element of honesty. As for Pinkie and Twilight, they were Beneath Suspicion because "The detective must not himself commit the crime."
No it doesn't. If Rainbow Dash was the one who kept her greed in check, people would say "This makes perfect sense. The Element of Loyalty wouldn't betray a friend's trust." Or Rarity "This makes perfect sense. The Element of Generosity wouldn't be so greedy." Or Fluttershy "This makes perfect sense. The Element of Kindness wouldn't screw over her friend and a pair of overworked parents."
The fact that Applejack doesn't do it showcases she has better self-control (and this would be in-character because she is depicted as being one of the most level-headed of the Mane Cast in most situations), but assigning her victory over her temptations to her status as an Element Bearer is to ignore how the others failed in theirs.
No it doesn't. If Rainbow Dash was the one who kept her greed in check, people would say "This makes perfect sense. The Element of Loyalty wouldn't betray a friend's trust." Or Rarity "This makes perfect sense. The Element of Generosity wouldn't be so greedy." Or Fluttershy "This makes perfect sense. The Element of Kindness wouldn't screw over her friend and a pair of overworked parents."
The fact that Applejack doesn't do it showcases she has better self-control (and this would be in-character because she is depicted as being one of the most level-headed of the Mane Cast in most situations), but assigning her victory over her temptations to her status as an Element Bearer is to ignore how the others failed in theirs.