In m3 I have 100k loot bonus which makes anything at least okayish really. So its mainly having really good loot (200k+ + 100k loot bonus) and sometimes just disappointing loot(100-150k +100k loot bonus).
Usually somewhere in between but for every 20 raids I do I get around 5-10 really good raids I guess. But no I feel it is mainly luck I don't think there are periods where loot is definitively better on a day-today basis, but after updates and maint breaks I do notice an actual change in the trend though.

