AO: My profession is "goat herder". I love my goats...
Max Nerheim is
not a goat herder. He knows what he's talking about, and he's proved that, consistent with the laws of physics, you don't need anywhere near 25,000 volts to get a spark out of a good spark plug.
The secondary coils in a standard steam driven magneto can indeed put out lots of volts. Lots and lots of volts.
It builds up and up and up until it finds a path to earth ....
That's what eventually kills coils.
I prefer to use plugs that put the least stress on the coil for the best spark.
A squared: As a matter of interest, have you ever paid for a set of iridium fine wire spark plugs out of your own pocket, and let someone loose on them with a 'gapping tool'? My guess is you haven't.