I can only see affliction rate up being useful if you're someone who only plays only 1 or 2 element teams or for a hime that has an affliction that misses a lot like Thor or someone using dizzy. For someone who plays all elements, you'll almost always have elemental advantage and having that increases your affliction rate (from what I've read), so missing afflictions is not a common ordeal to worry about for those that always have elemental advantage, even less so if you're using Mordred. So as someone who does, I can't see affliction rate up accessories being much help as I rarely have to worry about missing important debuff nor do I never rely on any low rate afflictions.