[Ace]

Well, for full disclosure, here's the problem with creating such a thing. It doesn't hold up for every FATE, and as far as I know, most FATEs will work out much worse if the bots are following this behavior. It is probably true there are a few FATEs in which the scenario you describe is true, and it works out poorly that the bot wants to target the boss, but more often, this isn't the case. Historically there are a number of FATEs which will punish you (think Cancer) for targeting adds instead of the main boss. To really make it work this work, we would need a solid list of which FATEs work better if lowest health is targeted as priority, and which ones need to focus the boss, which is no small task considering the number of "boss" type FATEs in existence.

Further full disclosure, this is how the FATE bot used to work, and people complained about it quite a lot, which is why it works the way it does now.