My first thoughts on reading the report were: why did the Captain leave the flight deck given the weather that must have been painted...even if he remained in the jump seat...as it was he returned to a chaotic cockpit, trying to play catch up on the preceding events. Also nobody has mentioned the well developed T-Cell that they descended into...even if they had reverted to basic power + attitude it would have been extremely difficult to hold an attitude in severe turbulence. And as far as I understand Direct Law still has roll-protection...making it even more difficult to keep wings level in severe turbulence. Plus it seems a greater diversion could have avoided taking them over the worst of it.... Strict Crew duty times and tight fuel margins may also be a factor here...