1. The first six Final Fantasy games were all 1-2 years apart. FF7 took three years, and then they were 1-2 years apart again through FFXI.
2. More frequent titles does not necessarily mean shorter development cycles. It could also lead to more titles in development at once.
3. Even if it does lead to shorter development cycles, this faster turnaround means that fan-feedback will more quickly be usable. If you figure they won't be able to put anything into practice until two games later, this could mean three years instead of ten.
4. Even if it does lead to shorter development cycles, this would require them to cut back on the single biggest time-suck in game development: graphics. Since you have previously stated that good graphics are to the detriment of good gameplay in a FF game, this should be a good thing.
This isn't really the same as annual Call of Duty or Madden games. These still need to be new games with new stories, and they need to focus first and foremost on the single player. They can't get away with releasing what's essentially an expansion pack at full retail price the way Madden or CoD does, because new releases don't render the older ones unplayable as tends to happen to multiplayer games, when nobody's ever online in the old ones after a newer release.
If anything, more frequent games should mean an overall improvement in the quality of the series. If it doesn't, they will destroy their reputation faster than was possible when the games were five years apart, and they know this.