I just have completed two of my ARR weapons and am on the next to the last step for the third one. While I was in the ATMA stage of my third weapon I decided to farm out every one I would need for ALL the ARR weapons when I went to do them. I farmed this for about five days 3-4 hours per day and got all the ATMAs I will need to complete every weapon.

Was it a grind? Yes, but is it bad? No. What I did was chat with some of the folks I saw at each fate and then formed a party.. we would go a clear a fate super quick and then head to the next one.. Doing it SOLO could be troublesome, but get a group together and the flow works and you will get it done..