Not always sir. For electric locos, you should consider the power transmission losses right from the power plant til the loco, which will involve 100s of km of OHE wire. When you consider all these factors, there is not much difference in the efficiency between a eloco and a disco.
There are a lot of factors which determine which is more efficient. IR is looking at one side of the coin and there are equally many more people who are also against electrification for the same reason. Its not easy to make a generalised conclusion in this argument.