but that ALL of those settings simply resulted in no change at ALL in the actual power generated by the engines - which remained at TO/GA?
Not true, RWA.
Page 113 of the interim report shows the engine power commanded by the crew (N1 Command), and the resulting engine thrust generated (N1 Actual).
The thrust is clearly not staying at TO/GA, but following the power level set by the pilots.
From CONfiture's post, I think he was specifically referring to the maximum power available during high-altitude cruise.