One thing to note is that on EY you are guaranteed full-flat, direct aisle access, 1-2-1 configuration in J (on all but short haul aircraft) whereas on EK J you will currently get the incredibly dated sloping 2-3-2 config on their B777, which still serves a good many long haul destinations. EK A380 is a different, much much better story.
EK’s 777’s aren’t the best ride in J but they beat out the EY A320’s operating many longer routes like MAA/CMB which I frequently fly. Also all of my long haul flying is to A380 destinations which EK has a growing number of.