I guess what is required is an engine indicating system based on EPR (or something similar) to better measure thrust, but where the 'EPR' is displayed as a % of the maximum.
This way you get a system that is measuring thrust but with a more clear indicating system.
EPR engines measure the pressure rise across an engine to define a thrust level. Hence, a fixed EPR gives a 'fixed' thrust independent of engine deterioration.
N1 records the Fan RPM, but this must be based on a fully deteriorated engine (just before it is pulled) to ensure that the certificated thrust is provided on every take-off.
So a new N1 controlled engine must provide higher thrust levels that deteriorate back towards the certificated rating. Issues include; i) increased deterioration and reduced lives; ii) potentially lower than rated thrust