Neptunus
"On seeing the UAS prompt......." The first input was NU, are you saying that was not an attempt to "SET PITCH" (at 5 degrees)?
"Why the much larger (larger than 5 degrees) PITCH UP?" Beats me, you are saying the "larger PITCH UP" was PF commanded? Not known.
"At STALL, the PF should have maintained ND". Not at all. He is trained to prevent loss of altitude. Cannot do that with maintained ND. The STALL warning is not STALL, something he has never experienced in this a/c.
"augmented by manual nose down trim". NO. They were not in the correct LAW to have been prompted: "Use Manual Trim Only".
"At least one simultaneous side stick input, which is forbidden" You are saying they were not attempting to maximize ss input to be certain they were at maximum deflection (authority)?
Without CVR (further) we cannot eliminate that this dual input was not sussed as a possible remedy for PITCH authority? That it was discussed, and attempted in spite of (horrors) it was forbidden?