In case you're as confused as I am about what happens with the devourer's armor in terms of it leveling or how the set bonus works, it only leveled to 20 for me after I defeated the Devourer and after I told the Dreamer I wished to leave the dreamscape (in DE version). However, after doing that, I noticed after my equipped level 18 breastplate "The Devourer's heart" which had 3 equipped runes on it, disappeared all the runes after it was upgraded. Let that be a warning to anyone who is currently used it on a STR character that you can and should remove the runes before you talk to the Dreamer and level the dreamscape area. Also I resisted and successfully passed the check on all of the visions but was still hit with 3 shackles of pain on my character. Not sure what I missed in that regard.