Careful with these assumptions, though: Did you wear hat/belt during farm? those 2 increase your shard generation quite a bit and you would not be able to wear both together with the chest.
Also: You're playing with the 4-set which again increases shard generation more than the new 2-set.
More shards available --> More shards spent --> perceived higher uptime.
Lastly, the pure fact that it is a Tier slot also would mean that this legendary needs to compete with the 2+4 set combinations vs. for example Prydaz, Belt or any of the rings.