Pegasi Physique (Patreon)

Rainbow Dash proudly shows off her hard-won physique! Cloudburst stands there and tries not to look terrified.

All three pony races have an "ideal" body type that is celebrated and pursued by members of said race. For unicorns, the ideal look is slender and delicate, with flowing fetlocks, glossy mane, and a long spire of a horn (basically an alicorn). Earth ponies like their bodies big n' chunky, as strength is prized for farm work and child bearing. The ideal pegasus, however, is compact, lean, and fast, with bright beautiful plumage. By pegasi standards, Rainbow Dash is a total knock-out and she knows it, she's very proud of her colors, speed, and power, and is still leaping to pose for Wonderbolts Weekly well into her golden years.

Cloudburst is another case. Pegasi are typically prideful and adore showing off, flight displays and wing flaring are common courtship tactics, with pegasi selecting the most colorful and charismatic mates. But Cloudy is drab. She's the color of a raincloud. She is small. She can't fly long without exhausting herself. While Rainbow has speedy knife-shaped wings like a falcon, Cloudy's wings are stubby and fluffy, like a chicken. Cloudy is a decent athelete, make no mistake, she's a professional level skateboarder and buckball player. But she's no Wonderbolt. Her size means she needs far less calories than the average pony, but like both of her siblings, Cloudy loves food, so she's a bit chubby. Her father Dumbbell has quite a lot of earth pony blood in him, and passed his bulk onto all three of his kids. Stormy and Phoenix got the muscle, Cloudy got an absolute dumptruck ass. Cloudy hides her curves under chunky hoodies and baggy clothes, she does not like being seen or allowing anyone (especially some random rude pegasus) the opportunity to comment on her body, especially not in comparison to her mother's or brother's. So Cloudy hides, even in stifling hot weather, and only comes out of her shell around ponies she trusts.

tldr:

Rainbow Dash: lean mean speed machine

Cloudburst: fat bottomed girls you make the rockin' world go round