@northern haste  
Well, my comment still stands, as Fluttershy also had a brother we never heard about for six seasons. Granted, she has a good reason not to bring him up, as he’s not exactly the kind you want to brag about.

@detction  
So you think that in season 1 showing Pinkie has only 2 sisters, then 3 whole seasons later there’s suddenly a 3rd sister in a family picture doesn’t seem ‘out of nowhere’ to you? Where’s the hint before that picture was shown? A non-canon novel(Pinkie Pie and the rocking palapalooza, or whatever it was called) which I only know about because someone posted a shot of the page referencing(but not naming) this third sister?
 

 
 
I’ll grant you that the issue is swept under the rug. When Twilight complains to him about not being told directly of the wedding, instead of answering he sidetracks the issue by asking her to be his best mare which distracts her and we never get an actual answer from him. It is one of the things that bugs me about that.
 
But presumably Cadance has known Shining since Twilight was a filly. Cadance is Celestia’s niece, and Twilight is Celestia’s student. They were bound to have met a few times when Twilight was dropped off. They could have kept in contact after Cadance stopped foalsitting her.
 
Or they could have reestablished contact after Twilight left for Ponyville, found they were still in love, and quickly decided to get married. Backstory is largely a main character privilege, so the history of their relationship is never going to be explored. There’s still so much we don’t know about Celestia and Luna, either.
 
Why direct all the hate at Shining, anyway? Her parents also never wrote her about the event.
 
Weddings usually take place a year or so after the actual engagement to reserve everything. If I had to wager a guess I’d say Chrysalis sped up the proceedings deliberately, so she might have tried to exclude the mane 6(or at least Twilight) as the Element of Harmony wielders. You can’t say she didn’t know about them, or they wouldn’t have been guarding the room where they were kept .
 
I also read a theory that Chrysalis herself planted the threat idea to get everyone focused on the thought of an outside threat so she could sabotage things from the inside and get Shining to exhaust his magic to allow her army in. Makes sense, since no one seemed to know what a Changeling WAS before she revealed herself.
 
We don’t know when exactly she switched places with Cadance, so she could have been manipulating things behind the scenes for a while. All we know for sure is that it happened after they agreed to get married.
 
Maybe it takes more effort than it should, since it relies so much on theory and off-screen interaction, but nearly all the things you’re complaining about can be reasonably explained.
 
And really, all writers are human. No one has ever had a perfect show or novel or video game. We all have gaps. I don’t see a need to get so heated over a kids show.

@N2MP  
also everyone has a mother and father but not everyone has a sibling

@N2MP  
Also, no. Maud is a better example than Shining Armor, because she was at least hinted at rather than brought out of nowhere just to sell more toys.

@N2MP  
Because Shining Armor’s introduction was awful.  
The conflict of Twilight feeling neglected is swept under the rug with this bullcrap excuse of being on royal duty, yet he had plenty of time to write to Twilight about Cadence, because, y’know, there would have been a falling in love phase, a dating phase, a deciding to get married at all phase. It’s swept under the rug with the off-screen interaction excuse, which is lazy writing. “Not mentioning =/= doesn’t exist” does not apply when the episode opened with the conflict of Twilight not being informed of such an important event sooner, when Shining Armor had plenty of time to do so before the threats were made against Canterlot. It is lazy writing.

@N2MP  
I never said they needed to but they had opportunities to foreshadow him

@northern haste  
I can understand the complaints about Cadance because THIRD ALICORN??? (Not that it actually bugs me) But I don’t get why they’d HAVE to foreshadow Shining Armor.
 
Not mentioning =/= doesn’t exist. How many seasons did it take for Fluttershy’s parents to appear? And Applejacks(through flashback) and Rainbows? Just because they weren’t brought up before their debut episodes did they never have parents? Should every character announce their family tree?
 
Twilight is a humble person and not too sociable. Her not going “Hey, I have a brother that has one of the most important jobs in the world” is perfectly in character for her.
 
Maud’s example is a little harder to swallow, because she actually DOES just seem to come out of nowhere. Pinkie had two visible sisters. Why not just make one of THEM Maud instead of seemingly randomly just creating and throwing a stranger(at the time) into the family photo?

@detction  
Wat? I have no idea what are you saying.
 
Alright first of I am not saying mistake and plothole is something “good”. But that’s not just the part of the story. There other polished plot part, how the character interacted, the build up, climax and others. Because that I forgot some of the plot hole, or even if I noticed it I don’t care that much.
 
“Oh I forgot… we’re in 2017 where everyone is self-righteous about their opinion like it’s law.”
 
Seriously what even is that? Are you saying that I am forcing my opinion as “law”. All I am saying is that you and I have different taste, what you find good might not be good for me.

@CyanLightning  
I gotta say, it’s concerning if people actually think mistakes and plot holes are good story telling.  
Oh I forgot… we’re in 2017 where everyone is self-righteous about their opinion like it’s law.

@detction  
Yeah, but sorry. What you think as a “good story telling” isn’t what we think as “good story telling”.

At least they actually foreshadowed her existence before actually introducing her unlike shining armor  

@Background Pony #E9CE  
People with actual taste in good story telling.

Maybe she just showed up to the party later?
 
Really, it’s not that hard to make it work.
 
Plus, she at least got to appear in a picture before her official debut.

Come on, it’s just a show.
 
Besides, Who cares about the mistakes in the show?