Need help understanding BiS(best in slot)

[Docent]

Edit: For example, I see this thrown around as "WAR BIS" a lot by people who don't understand priorities. See the glaring problem? http://ffxiv.ariyala.com/PQXT

Where to start?

Under accuracy cap for T13 (555/558), over accuracy cap for anything else in the game, and doesn't have the "minimum" of 390 skill speed recommended by DPS-focused warriors?
571 accuracy if the eat Caviar, which seems overkill. (Is that BiS supposed to eat Black Truffles, or god forbid, bacon bread?)
It's not using melded Platinum accessories, either...