The only thing that matters is that the WM dies, if he doesnt die no one cant orange, place on the leader board does not affect chances of orange. I have gotten orange placing dead last and placing first and anywhere in between, I have got orange when I didnt revive anyone, and when i revived 1 or more players. I have received orange doing 0 dmg and arriving moments before he was defeated. Its all RNG.
Soonish as someone else said when they fix the loot tables providing they dont somehow break another aspect of them you should be getting orange much more often since they are removing blue and green drops for defeating him.
I have pulled about 50 orange myself, and still havent gotten one of all types. Seems for me personally Area suppressors and Triple shots / breachers are all im destined for.
Ive pulled 5 splitshots, 8 tripleshots, 4 breachers, 6 area suppressors, 4 corpse infectors, 3 volge recon, 2 typhoon x, 1 quickshot blaster, 1-2 monitor sidearms, 2 quickshot pulsers, 4 crankshots, 2 headshots, 1 corpse infector, 3 zaggers(no 4 bangers

), 4 clustershot cannons
0 clusterdrops
0 needlers
0 springers
0 precise chaos
I probably left some out but he certainly drops a lot and with the upcoming change I suspect he will drop even more.