We have a massive side quest about Yuffie, meet her father and learn how Wutai was plundered by Shin-Ra. We learn about Vincent's past with the Turks and Lucrecia. We visit Red XIII hometown and learn about his father and his race.

We learn about every single character in the game, apart from Cait, who is really Reeve. It is very unfair to say it all revolves around 3 characters when it plainly does not. Obviously they are the MAIN characters, but that is to be expected. You can't tell an effective story if you are constantly finding silly reasons to get them all involved.
Lol. So it takes a measly side quest to know about these characters. Vincent's Lucretia sidequest was so minute and unrelated to the whole story. In Final Fantasy IX, everyone's story was part of the main story. You didn't have to go out of your way to find out about these characters. They naturally blended in with the main quest. IX did a great job getting all the characters involved and still had a great story. Main characters in a Final Fantasy story should relate to all the other characters. That's what makes them leaders.

This is to do with the silly translation. It is much clearer when you know the actual dialogue.
The problem was that they tried to make this scene so sad and emotional. If we knew a little about Cait Sith and his story, it could've made his sacrifice more powerful. It's like they tried to play it too safe by having the one character with no back story or past or anything the sacrificial lamb. Honestly, it would have been better if the new Cait Sith never came along. It would have been a little more emotional.

Cloud isn't supposed to have. He is a cold hearted mercenary. Making him suddenly social machine 2000 would not be his character anymore than it would Squall. Also, there is a limit to how much story telling you can do in a game.
I'm not saying he should become social out of nowhere. But in a good storytelling game, we should be able to see a gradual change in the character. It's called character development. No character should end the same way he began.

This is simply inaccurate. You find out all about Yuffie and her peoples past, you visit her home town. Same with Red XIII. Same with Barret (there is even dialogue about his wife and why he hates shin-ra). You learn about Vinent and his past (again having too much dialogue with Vincent or an Auron damages their character). Every single character had a full backstory except reeve/cait sith.
I understand that each character has their own story, but I want to see some change in the character. That's what character development is supposed to be. It's like they all have the same motive all the way to the end of the game. In Final Fantasy IX, we see how each characters are not the same as they were. We see how traveling with Zidane gives them a new outlook on life. We see how Zidane fixes each character's flaws. That's the type of impact a main character should have. Yes, too many dialogue for certain characters can ruin their whole character. These characters are usually the type that has very little to say but when they say it, it's a very deep and meaningful sentence.

That might just have to do with the fact he was stopped by your party, which was the object of the entire game. He almost destroyed the planet.
The fact that he was stopped by the party before he accomplished anything just shows how overrated he was. Kuja's accomplishments overshadows Sephiroths accomplishments. He destroyed Alexandria, Cleyra, Burmecia, and Lindblum. 3 of them he used someone else to do it. He achieved the power of Trance. He killed Garland. If that wasn't enough, he destroyed an entire planet. And after all the havoc he released on Gaia, the party stopped him before he delivered the final blow. See the difference? How a villain looks or dresses or what theme song he comes out to shouldn't make a villain. His accomplishment should. Which is why I say Sephiroth is overrated.

A game that had far less character development than VII and far less dialogue overall.
Less character development? Ok. The main character was involved in all the characters problems. He made their problem his own. Amarant had a whole new outlook on teamwork. Steiner changed his loyalty towards one person into a whole nation. Eiko, who was always alone, found the meaning of friendship and happiness. Quina who was isolated in her little marsh faced his/her fears and went out into the world and experienced many different things (and Quina is supposed to be the Cait Sith of FFIX). That's what you call character development. Dialogues? We see these changes in characters through their dialogues. The meaningful dialogue between Freya and Amarant (rivals) during their fight with one of the 4 fiends, showed the change Freya saw in her rival Amarant. Or any dialogues between Steiner and Vivi shows the whole master and servant relationship between the two. The comedic dialogue with Quina and Vivi or Quina and ANYBODY for that matter. Or the dislike Steiner shows Zidane through his dialogues and movements. See how not one character is secluded unlike Final Fantasy VII?