I don't think FFXII had the most unrealized potential. In fact, FFXII may be the one FF that fully realized its potential. That doesn't mean everyone will like it. It's unique among the single player FF games, the most unique FF since FFII. Both FFII and FFXII are near the bottom of my list of favorites because I didn't like the directions they went.

Not liking a game is not the same as it having unrealized potential. A well-made, fully-realized game will still have people who don't like it if the actual gameplay doesn't appeal to people.