This is without any sort of minmaxing, just using what I have lying around not changing enchants or azerite traits or using foodbuffs/stat flasks.
Buffs active at that moment in the screenshot:
Celestial Alignment (15% haste)
3 stacks of Starlord (9% haste)
22 stacks of Overwhelming Power from 2x 480 azerite pieces (1496 haste rating)
16 stacks of Void Ritual rank 2 (528 haste rating)
Mallet of Thunderous Skies (35% haste)
5 stacks of Condensed Life Force (10% haste)
10 stacks of Essence of the Focusing Iris (400 haste rating)
40 stacks of Blood of the Enemy (709 haste rating)
Vita Charged (1674 haste rating)
Humming Black Dragonscale (442 haste rating)
Racing Pulse rank 3 from 2 pieces (2550 haste rating)
Combined with 33% increased haste gained from Expedient corruptions.