Rainbow Dash gets too much focus and special treatment compared to the rest of the girls minus twilight, she's a creators pet at this point. And by far the most important of the mares in support, skillset, and overall power. Especially in power where she's basically a anime hero and second only the twilight in being the most capable in battle or solving head on problems with strength, speed and determination when twilight herself can't do it. She and Pinkie are the icons of the show and even this forum displays her as the main draw for casuals to become mlp fans.
Really her existence inhibits all the main six even twilight in being as cool or entertaining as her because she's the easiest character to write for fans and appeal to them(Even twilight sometimes can't come close RD's IT factor). She's badass, charsmatic, tough, sarcastic, carefree, and fearless. Flawed and not the ideal role model but she's still a adheres to the themes of the show in her own way. This makes her friends seem too boring and vanilla, because she's the only one who is allowed to be the stand out, be the edgy one who does the rebel stuff, the unconventional star that strays from feminine cliches and brings the new hardcore elements that men and normal down to earth girls like. She also has to learn from her own flaws the most since she is a stand in for the kids who get careless about their actions as well as be treated as a troublemaker who everyone thinks her antics are going too far.
While people like Applejack, Rarity and Pinkie Pie play roles in static amounts and just come off as tedious plain main heroines that really bring nothing but idealistic facets of moral imperatives and hardly get reprimanded like Rainbow because she has the anti mare and thusly the most imperfect. Why should RD be the most flawed and prone to bad habits, Pinkies to innocent and goofy to have RD's self interested callousness even though she's as mischievous and prone to seeking excitement, Rarity has a composure and elegant allure of consideration but she's Arrogant, Conceited, and Self Assured as RD, Applejack is a just well adjusted all around and is more mature than all the ponies but she thrives on pride, ego, and greed. She and Rainbow are like two sides of the same coin. Rainbow is wild and non accountable to Aj's cool and responsible but they both have the same beliefs in being the best and pride.
I wish the girls had Rainbow Dash's conscious imperfect traits, or at least where all equal to her in being able to take to the action in their own way.