Owain: thank you, a light went on as you described the gains and input relationships, and responses.
Retired F4:
This sluggish behaviour in pitch would be a new expierience to PF, especiually when the roll channel behaved quite differently (more agile).
Some years ago, I experienced a somewhat disorienting moment in the cockpit when the SAS and trim in the lateral channel went awry while the pitch channel remained just fine. We disabled AFCS and flew AFCS and SAS off (which required a gentle touch ... but is also something we used to practice!) once we figured out what was wrong. It "felt" wrong to say the least at onset.
I suspect that PF in AF447 encountered a similar "wrong" feeling, if the graphs depicting his efforts in the roll control are any indication.