I was getting around this deflection on my Unbroken/Trickster (Def. 169) and I still couldn't solo tank the Famypr cave (they were hitting me enough to get thru, especially if I got flanked). Even chugging potions and castin a few Moonwells (where the Deflection was supressed for some reason) didn't allow me to kill them all before they killed me. Nemnok cave facetanking was slightly better but still not easy. I could really use some help finding a better build that won't get hit - it seems on PoTD they crank up enemy to-hits so much .... also Mirrored goes away after even 1 hit gets thru .
As I completed my PotD Solo (Triple Crown + Magran Challenge + Berath Challenge) playthrough recently, I can share my experience with a herald. A had around 130-140 deflection, build focus was healing with Ancient Memory / Exalted Endurance and killing with summons. Nemnok is easy - there you can facetank everything. Fampyr Cave / Splintered Reef are more complicated, because you need Acolyte's Frostbite for free Concentration and Modwyr for Intellect affliction immunity. Getting Charmed/Dominated is annoying, because the Enemy AI often changes your Paladin Aura ... so you have to switch your weapon sets a little bit. Sometimes when you get damage spikes you need Greater Lay on Hand or Healing Potions, but in general its really easy with this class. It is not a build that won't get hit, but it is a build that survives this kind of stuff.