You need to do a bit of calculus on the flight profiles to get the total emissions from point A until point B.
Less power low down means the time taken to get to point B increases and the fuel flow reduction from increase in altitude is not seen for a longer period.
Until the extra fuel burned is more than the maint cost of doing full chat departures all the time reduced thrust is here to stay.
The airlines will be quite thankful that most environmentalists don't really get that all calculus does is let you work out the area under a wiggly line in a graph.