But what I don’t understand is the comment about 21st century autothrottles.
A/T on most other aircraft built in the last 30 years remain on and you only have to push a button or move the thrust levers in the case of Airbus to set GA Thrust. Why can't the 737 be that simple? And yes it may actually be a policy issue rather than system design.
... at full thrust? Ahh, no.
If you set some sort of 'average' N1 figure for a reduced ROC GA and something happened as a consequence I would suggest it would not look good in the subsequent safety investigation.