I dont think its an exploit. The mobs people farm are intentionally placed seperate to the Lambs, and they dont contribute toward completion. I guess it sounds kind of bad describing it but, it's not a bug, people are playing by the rules and are choosing to advance this way. It's just like in FFXI with abyssea XP alliances, I highly doubt abyssea was designed around that, but players used it and it wasnt against the rules.

The issue with AK speed runs is that people were skipping the majority of the dungeon, nobody's skipping killing the target enemies to complete this fate, they're just choosing to wait until the timer is nearly up to do so.