...are people forgetting a little game from nearly two decades ago called Final Fantasy VII? >.>
Because the way I remember that game, you only got the full backstory about the guy Cloud modeled himself after if you went to the basement of the mansion in Nibelheim unprompted, and there was a party member who you could miss entirely even though he was more tied up in Sephiroth's backstory than anyone other than Cloud.
With that said, I think what FFXV is trying to do might be a bit different. Its core ambition is "road game," and that means focusing on internal development and relationships between traveling companions more than external plot development. And while there's no way to know how well that's executed until one actually plays the game, it does seem like "the party dynamic is great but nothing happens" is exactly the sort of reaction one might expect if someone went into that sort of game expecting something more plot-heavy.
(I'm of the opinion that, however it turns out, FFXV is going to be fascinating to analyze.)