magic rainbow sparkle horse

Earth ponies are almost always expected to be providers. Like the Apple family for example or the Cake family OR even the "flower trio". They provide necessities, often food or they often provide hard labour (note how "background" jobs like construction and taxi pulling are most often done by earth ponies too). Applejack is obviously a perfect example of this! She's the head of her family, she's extremely hard working, shes incredibly physically strong, she's known and relied on by most of Ponyvill. Applejack very much lives up to the expectations that pony society has of earth ponies.

Pinkie Pie on the other hand is not one bit concerned with hard work. Her whole thing is having fun and throwing parties. In a way she is also providing something very important and necessary, socialisation and relaxation, however these are generally not deemed as valuable as strenuous labour and food production. Pinkie Pie is always written off as "childish" or not taking things seriously enough. She isn't deemed as very reliable a lot of the time and has to work very hard to prove herself, more so than someone like Applejack.

Ponyvill was founded by earth pony farmers, and is densely populated by earth ponies. Earth ponies are expected to work hard and grow food and provide for everyone, their roles are incredibly necessary and their work is highly appreciated. However, without someone like Pinkie Pie who deviates from those expectations, Ponyvill would be a miserable place (as seen in the episode Magical Mystery Cure). She may not be a farmer or a construction worker but her divergence from earth pony "standards" is what keeps everything in balance.

The same can be said for Rainbow Dash and Fluttershy too. Rainbow Dash is an exceptional athlete, she flies like no other pony and she almost always has her wits about her. At the end of the day, Rainbow Dash is truly a performer at heart, she wants to be in the Wonderbolts and show off her skills to all of Equestria. Pegasi are expected to be fast, agile, eager, always cool, proud and quick witted just like the Wonderbolts, and just like Rainbow Dash. She is a peak performance pegasus.

Fluttershy is Rainbows exact opposite. She doesn't care for speed, adventure or displays of athleticism, she truly doesn't even care for flying. She is, in both a literal and metaphorical way, very "down to earth", however her role is still very important and her being a pegasus is still very integral to who she is. If it weren't for her experiences of being ostracised for being different she would never have the empathy and dedication to her animals the way she does (and on more practical note, being able to fly does aid her in her work a lot the time). Fluttershy slows down, she's quiet and she gentle which something that other pegasi (and earth ponies honestly) struggle with. It was alway right for Fluttershy to be a pegasus who could soar the skies, because if she never fell down to earth she would have never found her true calling. Without ponies like her, many important things, creatures and events would go unnoticed and unchecked.

Rarity and Twilight Sparkle is kind of a funny one because I think a lot of people may expect Twilight to be the prime example of unicorns, but that's not really true at all. Twilight, despite being our mane character, is actually the deviant one here.

This is illustrated for us almost immediately in the first episode, where she's invited to a party by three other unicorns but ditches it to go study instead. Magic is merely a tool for most unicorns, but for ponies like Twilight or Starlight, it is their whole existence, it's what they were quite literally born to do. Twilight does not value social status at all, she doesn't have time to and growing up so stuck in her studies I'm not even sure she aware that it's such a big deal to others, especially within Canterlot. It's also worth noting that to Twilight, Princess Celestia was always her teacher and Princess Cadence was her babysitter so their status as royals never really mattered to her and she's able to see them more are regular ponies for that reason also.

Most Unicorns are socialites, they value "social currency" and monetary gain more than they value magic. They don't care that the Princesses are very powerful magically, they care more about their political powers and their social status as royals. We see this clearly in the season 2 episode "Sweet and Elite" where Rarity gets swept up on the high society life of Canterlot, when she mentions being from Ponyvill to two random snobby unicorns they look down on her, yet once it's revealed that she's staying at the castle for her visit, things change, mostly notably: her status. Rarity is a prime example of a unicorn, she's stylish, she's ambitious, she's concerned with image, she's social, she has very fine tastes and she's a businesswoman.

As the series progresses we she both Twilight and Rarity gain some fame. Twilight is mostly inconvenienced and troubled by this whereas Rarity, like most unicorns would, relishes in any sort of limelight. Unicorns are expected to be professional, they're most often more modern or "ahead of the curve" than other ponies and tend they to be the primary business owners of Equestria. However without ponies like Twilight, magic would become just an afterthought. Without powerful wizards like Starswirl, dedicated students like Subburt or magic obsessed freaks (affectionate) like Twilight Sparkle, pony society would crumble.

Applejack, Rainbow Dash and Rarity are prime examples of what is expected of earth ponies, pegasi and unicorns, respectively, in Equestrian society. However without ponies like Pinkie Pie, Fluttershy and Twilight Sparkle there would be no balance and no progression. In fact in the episode "Hearts Warming Eve" we literally get canon lore telling us that if it wasn't for three ponies who deviated from the rules and expectations of their respective tribes, that Equestria wouldn't even exist today.