@believer258: I don't believe anyone in this thread claimed that the game forced you to fight every boss again. I'd say as people who have actually reached that point in the game, we're all well aware of what the game is asking.
The real issue with the last four chapters is that it defies the brisk pace established by the first four. For about 40 hours, the game does a nice job of motivating the player with the promise of new stuff: new environments, new equipment, new bosses, new jobs, new scenarios. The last four chapters state pretty up-front that it has exhausted its supply of new stuff, which is why many people in this thread seem to have lost their motivation to continue.
Regardless of how quickly one can blaze through the crystal scenario four more times, that doesn't change the fact that the game has essentially turned itself into a chore. That is, as you said, bad design.