He was using Malleability, which means no corporeal hardening, no calcification, etc. He also used this to dodge a number of attacks.
His edges, combined with your use of imperial offense and metabolic quickening, is pretty much a recipe for 0 defenses. I would be glad if I dodged any hits while frozen like that :P
It does seem you didn't hit a lot there, and should have hit more. I'd be questioning if your enhanced reactions was perfected, or if there was another factor adding to your poor ability to pierce his defenses. I don't expect a sword vs a hasted staff to do great but the flail should have been alright.
There's always RNG on your offensive part, but from the Muter's perspective that was pretty much the expected outcome. The fact you got 3 high maledictive neuros pre-neuro changes (which were only made last November) with those saves says something is fishy but I still want to see a more recent log to prove it. Maybe time to go pwn me some with perfected neuro.
Yhorian