Also, while I don’t recall the exact numbers, Ralph has stated in some past threads that he has observed remarkably high levels of energy emanating from LOMC cartridges at ultrasonic or RF frequencies.@almarg
The Hagerman site shows a 30db(!) peak. I can confirm that.
About 35 years ago I used to subscribe to the cartridge-needing-a-load theory. I set out to build a device that would come up with the correct loading so as to eliminate guesswork on the part of the user, which I was hoping to build and sell.
What I found when ringing the cartridges was that they really didn't ring until you got to some very high frequencies well past audio! This is easy to understand- if you pass a squarewave through one, there isn't much inductance to mess with the squareware at audio frequencies.
So if the brightness of an unloaded cartridge isn't due to ringing, what is doing it? I was lucky- a serendipitous event caused me to realize that the preamp played the bigger role. At that point it became a simple engineering task to insure that a phono preamp design would be resistant to this sort of problem.
In a way, I did get what I set out to achieve- being able to sort out the correct load, which for all LOMC cartridges is 47K. What is needed is a preamp that is unperturbed by a 30 db peak 100KHz or above into the low MHz.... Not that hard once you know what's afoot.