Final Fantasy XIII was bad, but Final Fantasy XV literally had core parts of the story locked behind [initially] paid DLC. It was a rushed, unfinished product which automatically makes it worse than Final Fantasy XIII.
Examples of bullshit storytelling:
The fall of Insomnia and the political setup of the entire war isn't explained in the game at all. You only know about it if you watch the prequel movie, Kingsglaive. While the movie is, admittedly, pretty awesome, this shouldn't be necessary to understand the driving force of the game you're playing. The treaty, Regis's death, Luna's role as an oracle, and Nyx's death/sacrifice can only be found in the movie.
Noctis's relationship with Luna is supposed to be an emotionally moving setup, but their history together and why she matters at all is largely shown through Brotherhood: Final Fantasy XV. When she died I didn't care, because the game itself didn't make me feel like she mattered in any way.
After Altissia, Prompto becomes withdrawn and reckless, and he eventually says he is "not like you" before being knocked off the train. None of this is makes any sense with anything the game shows up up to that point. Prompto's DLC reveals that he was engineered in a Magitek facility. Basically, he was a test-tube baby who escaped as a child. That knowledge reframes his entire personality, and his breakdown makes sense rather than him being melodramatic in the base game. Without the DLC, he just sounds like a lunatic all of a sudden.
After Chapter 9, Gladio returns from an unexplained absence with a massive scar, and he is openly hostile toward Noctis. In the base game, it looks like he just suddenly become a douche for no reason while Noctis was grieving (even though we don't care that he's grieving because nothing in the base game explains anything or makes us give a shit). We're given no justification beyond vague "you need to toughen up" rhetoric. Gladio's DLC shows that he voluntarily left to go through some trial tied to his family's role as shield of the king. He fails, almost dies, and this trial makes him believe that Noctis won't survive unless he is forcibly hardened. In the base game alone, it comes across as Gladio undergoing a personality change (just like Prompto!), seemingly for no reason.
You fight a Marlboro, and then the next thing you see is that you're on a train and Ignis is blind. No explanation is provided in the game whatsoever. In Ignis's DLC, which takes place during the Altissia incident, we see that he uses the Ring of the Lucii to protect Noctis. Because of the Kingsglaive movie, we know that anyone not of the royal family who wears this ring will be injured or killed. He knowingly accepts permanent damage so Noctis can continue toward his fate. In the base game, he has a calm acceptance of blindness that feels unnatural and implausible. With the DLC context, his acceptance of blindness makes sense, because he willingly sacrificed his sight for his friend and king. That's emotionally compelling, and you don't get this in the base game AT ALL. I was so bloody confused because I don't play DLC until I finish the main game, and there's nothing that says, "Stop playing this game now, and go play X DLC to figure out what the hell is going on with the story."
Final Fantasy XV is a fragmented Frankenstein's monster of a game, and nobody should defend this.
