Remember that ilvl (item level) does not always equal what I've been calling "rlvl" (Recipe Level, though it turns out the game uses that term for something slightly different, so I've deemed their Recipe Level to be "Craft Level" ("clvl")). The rlvl is all that matters for desynth, not the item level. otherwise, those Bridesmaid's shoes (which are i1, but r70) would have been desynthable by anyone, not only people with high LTW desynth, and they would have dropped no demimateria at all.
That Mythrite Halfhart Saw, despite being i85, is r125. You'd need a skill of ~110 to start on that.
And yes,
that item is desynthable.