you rightly captured many points in your answer, but some clarification is needed.
firstly, a 100 MW plant producing electricity is far more efficient and cosst effective than 25 4 MW plants doing same. A diesel loco is basically a diesel powered generator, or a diesel-electric as we call them, so when you replace diesel with electric traction you basially remove 25 4 MW diesel plants and replace them with a single 100 MW plant which s better in many ways. A diesel loco also has poorer power to weight ratio and high power corresponds to high torque, not just 200 Kmph+ speed.
The...
more... only issue with electrification in India is mindlessly electrifying lines with zero freight potential; thats a severe loss making proposition and i feel that for this line RoR will mostly be -ve