The fate is being done as designed, to some extent. Did the devs plan that we would farm mobs till 2min left then start killing the lambs in the back? Likely not, but until they say that it is not intended or not appropriate their is absolutely nothing wrong with it.

This FATE has been being used in this way since a few days after the start of Early Access and I am sure that the devs are aware of it. If they truthfully had an issue and felt it was an exploit they could have and would have simply moved the location of the lambs (all separate in the back) to be evenly placed throughout the FATE area so we could not just skip them and farm.

next people are going to say farming the mine (where this fate is located) between fates is also an exploit since one strong AOE group will claim and kill everything so quick that no one else can get exp here between fates.