Why N3 and G3 would change later superstructures

Would an N3-G3 building program bring the King George V-style superstructure into service earlier?

Probably not; Nelson's structure was already a reduced N3-G3 form, and pre-radar visual rangefinding encouraged designers to keep important equipment high above the water.

Building N3 and G3 changes the design lineage, so the later King George V structure does not simply arrive sooner. Nelson and Rodney already carried a cut-down version of the earlier concept. Before radar, height improved visual identification and rangefinding, giving designers a strong reason to raise directors and supporting equipment. Later radar rooms and combat-information spaces could alter that arrangement again.