Not getting at you, but this quest was very sloppily written and designed.
You do get a page for each. It’s a pity the quest doesn’t say that.
Collect Torn Pages of “Fear and Flesh” from Corrupted or Lost Areas within Horrific Visions for Wrathion in the Chamber of Heart.
2 Torn Page of “Fear and Flesh” (2)
Description
Another tome written by one lost to N’Zoth’s madness. I dread to think of what vile words await us within it. But if we are to strengthen your cloak, then we must know more of that which it was meant to resist. See if you can find the remaining pages so that we can complete this tome and make use of the knowledge it holds.
When I did this, I had no idea that one boss didn’t drop both, and/or that I didn’t have to finish Thrall. Actually, no, they don’t drop them, do they? I was confused by that as well. I killed the section boss - why haven’t I got a page? What do I do now? Not the greatest design when faced with time pressure. What possible sense does it make for the boss NOT to drop the quest item you were sent for?
So I burned a Vessel doing the wrong thing, because I couldn’t get any more until I handed that quest in, so I had to use a run for just one of the areas. Not a big deal, really, but the sloppiness of the whole thing bugs me. It was completely unnecessary if they had written clearer instructions.
I need to read some guides and watch some videos, apparently. I spoke to an in-game friend who is not even as clued in about it as I am, and who did a vision, had no idea what happened, and came out with nothing.
And incidentally, I read that Lost area bosses don’t drop these pages, so if you got Lost and braved your way through despite that, and despite the explicit quest text, you came back with nothing.