Here is the story:
I have done the Dusk Palace strike many times in the past weeks. Level 36 playlist and heroic playlist. Never got a Flayer mantle. It was frustrating.
A forum member gave me the tip to try farming the nightfall strike for the mantles. He said he got 2 mantles out of 4 nightfall completions. The first 3 times I didn't get one (done with each class), the 4th time, with my Warlock, I got the arc Flayer mantle.
I recommend farming this nightfall strike if you want a Psion Flayer mantle. Seems the Flayers are generous this week. Good luck.
Edit: Of course I don't know if the drop rate actually is higher on nightfall. But after trying to get a Flayer mantle for weeks without success on 36 and heroic playlist and now getting one after my 4th nightfall this week, I do think they are higher. If your RNG luck would suck ass like mine, you would probably think the same. Also I got 3 Treads Upon Stars from 4 nightfalls. Anyways, worth giving it a try if you've tried to get a Flayer mantle without success in the past days and weeks.
Edit 2: After another ~8 nightfall strikes I got the void Flayer mantle.
Edit 3: After another 5 nightfall strikes I got the solar Flayer mantle.
-
Here is why this works now.....legendary engrams used to be a drop for nightfall when killing the boss, they took this out, but left in the strike specific legendary items. Therefore smaller loot pool=more drops. So bungie did not raise the drop rate, but because the pool is smaller of what can drop, they are dropping more often. Essentially strike specific gear was the little fish in the big pond of items that could drop, but is now the big fish in a smaller pond of items that can drop.