You are correct - this will only produce useful energy, if you are near a broadcast transmitter.
I've also been a ham since the early 1970s, and have seen these circuits being promoted for "free energy". Most people live near a transmitter, and they may produce tiny amounts of current-limited useful energy. But if we have a major event, taking out the power - then the transmitters will mostly go silent - and no energy would be harvested.
Back when Tesla got into this, he was using his tesla coil to transmit the energy in the ELF freqs. But without the coil, it's usefulness fades away. BTW, semiconductor diodes did not exist in his day, so this circuit wouldn't have been "invented" by him, except as a theory. Vacuum tube diodes would not be useful to harvest free energy, due to wasted power for filament.