Rarity was inspired by aspects of Canterlot, which is where Celestia and Luna are, and the stained glass window of Twilight. Cadance rules over the Crystal Empire, and Rarity was making dresses to mirror aspects of Canterlot, so she wasn’t included.

@the metal bronyhead  
Why? Nothing that kid touches is gonna last more than five minutes.

Now make one for Flurry Heart

She made your wedding dress. Then she remade it after she found out it wasn’t you wearing the first one.

Uh you do a battle armor Cadence you are Warrior Princess

@CardStock  
…but being a Mary Sue isn’t based on perfection. Being a “Mary Sue” is based on more devotion to the character at the expense of the conflict and the other characters. Considering what you said about her lack of development, that seems to imply the opposite: that the writers need to put more thought into her character and give her more of a personality than just “perfect pony princess”.
 
Also, characters can exist as ideals. Heroes like Superman and Davey Crockett are ideals, and yet they don’t get slagged on because of a lack of flaws. Celestia could also count as an in-universe ideal character: there are plenty of ponies who hold her in high reverence, seeing her as “perfect”, yet we know already she isn’t.

@CommanderHurricane  
sorry that was Teddy Long who said it

@the metal bronyhead  
I did a spit take when I read that.

@CommanderHurricane  
In a TAG TEAM MATCH PLAYER

@the metal bronyhead  
I want to see Twilight and Celestia take on an opponent together.

to be honest i think Cadence and Celestia are just underrated MLP Characters do you all agree

@marinus18  
well she lived in Canterlot when she was little

I also think Cadance needs more. I really want an episode where she shows more personality.

Well Cadance isn’t from canterlot.

@I don’t know…  
CARNALITY!

@441TheSecond  

 
FLAWLESS LOGIC

who needs dresses than we got her in badass armor  

I was gonna say something, but I see there’s already an adventure in the comments.  

@CardStock  
True. Cadence has virtually no flaws and is loved by everybody.
 
However, you’re missing the one bit that makes Mary Sues what they are: Plot involvement. A Mary Sue will have the entire plot gravitate towards her. Every relationship, plot point, and nook and cranny in the story will be about her, she’ll always elicit strong reactions within all characters and characters will not be allowed any action that doesn’t directly link back to her.
 
Cadence is not that. She doesn’t overtake any episodes that she’s a part of. In fact, she hasn’t done much in most of them, and in every episode that she appeared in, the focus was still largely placed on another character.
 
Bottom line: She’s not a Mary Sue. She’s boring as fuck, sure, but not a Mary Sue.

@CardStock  
Uh I don’t understand you a bit are you trolling us if you don’t like Cadence that’s fine for you but She’s not a Mary Sue

You’re wearing it.
 
The Princess of Love don’t need no dress…

@Joshua  
Yeah…I think she shot me…

@CommanderHurricane  
Wait! I think I just heard the sound of shots being fired.

Cadence: Where’s my dress?  
Me: I think it’s called Lingerie.

@elvis jeger  
Since when is Cadance as old as Luna and Celestia? She is around the same age as Shining, did you forget that she was shown as younger when she was Twilight’s babysitter?