Yes,efficiency of t/f is high.
To transmit power to long distances the losses in the transmission line should be less.
overall losses in transmission should be low.
and at both ends of transmission line we are having transformers for purpose of stepping up and down of voltages.
because transformer having less leakages as the core is made up of crgo steel and type of winding connections eleminates major harmonics.Main point to notice that "manufacturers design the transformers nearer to ideal conditions" which makes transformers to work at high efficiencies.
ideal conditions:1.zero losses 2.infinite permeability (i.e.,crgo steel is having high permeability)
3.resistances of t/f wdng is zero 4.Magnetization curve of t/f is linear