The things people will do to avoid putting up catenaries truly are wild.
This train on the other hand seems superior in every way for this specific use case (getting ore from high altitude to low altidude and empty trains back up)
Either way it sounds brilliant, both simpler and better than catenaries, I like it!
They also didn't have the same kind of battery capacity as we have today.
Electrified rail avoids shipping the engine and the fuel with the load, which ia often a big win in efficiency.
As for your swimming in money comment, I'm not sure what you mean; the Soviet Union was an industrial powerhouse and the second largest economy in the world between WW2 and the mid-80's, its economic decline only started after that with economic liberalisation under Gorbachev, followed by both oil price collapse and the costliest disaster in human history (until then), the Chernobyl incident, both in '86. Japan overtook it as the 2nd largest economy only by 1990.
Statistics about the Soviet economy are notoriously hard to make sense of. First, they ran a rather weird economic system (compared to the west), and second, you can't necessarily trust the statistics, there weren't really any independent organisations at all like we have in democracies. No independent media to check, no independent statistical institutes etc.
Even in the west environmentalism was only just getting en vogue in the second half of the 20th century. But the Soviet Union takes the cake in terms of how much environmental damage they were willing to take for a bit of extra economic output.
That $50mln would maybe be enough to electrify a single, 40km track.