The secret to a great amplifier...

As noted above, I am all for people testing fuses, just test them, with only your ears, and not your eyes. Get someone to help you so you can eliminate bias. Then maybe we can put this topic to bed.

By the by, there's a video on YouTube by Paul McGowen where he talks about fuses and it meets your very same requirements. In it, he tells of a friend of his who's doing something to one of his amps away from Paul, who's sitting some distance away, both talking audio.

Now Paul has no idea what his friend is doing, who tells him to just sit there and listen. Paul never knows if something is being changed or not, when prompted, or what it is that's being changed. Every single time he's asked if he hears a difference for better or worse, he's correct in his assessment. 

Turns out his friend was swapping out a fuse.

All the best,
Nonoise

This is Paul, who is no stranger to hyperbole, sort of like your description.

- A single change was made. The unit was turned off, said change was made, then turned back on.  There was no repeated testing.

- Paul say's marvellous improvement

He is already preconditioned for their to be a change. The expectation is already set.  This is what audiophiles do to themselves all the time. A real test would be changing the fuse between two different ones, and sometimes not changing at all.  It is not a subtle difference.

Of note, power cords likely taken on / off wiping contacts, case top removed to change the fuse (was it left off) ... oh, and Paul knew he took the case top off, so further expectation bias.

    Cargo cult science is a pseudoscientific method of research that favors evidence that confirms an assumed hypothesis. In contrast with the scientific method, there is no vigorous effort to disprove or delimit the hypothesis.[1] The term cargo cult science was first used by physicist Richard Feynman during his 1974 commencement address at the California Institute of Technology.[1]

Cargo cults are religious practices that have appeared in many traditional tribal societies in the wake of interaction with technologically advanced cultures.

     Do a bit of research and you'll learn those primitives were limited in their understanding of what they saw with their eyes, based on their prior experience, education and BIASES.

                                                A rewind:

                 It isn't that the Denyin'tologists are ignorant.

               It's they're knowing* so much, that's WRONG.

                       *heart of the Dunning-Kruger Effect

                                              OR, two:

     The Church of the Naysayer Doctrine (like every other faith-based, religious cult) has as many dopes as it does Popes.   

     Bring up anything resembling SCIENCE/PHYSICS, dated later than the 1800’s and they become apoplectic, not having the formal education to comprehend the concepts, or- possible ramifications.    THAT would be hilarious, were it not so pathetic!        

           Gimme That Old Time Religion, Gimme That Old Time Religion, etc.

        At the very first mention of something as simple as Wave Function (a BASIC tenet of Quantum Mechanics), the Cargo Cult will label you a KOOK.

        But remember: they can only view/understand you, based on their limited experience, education and BIASES.

         They have overlooked the fact that, if not for the hypotheses/theories and experimentation, regarding Quantum Mechanics: a plethora of modern conveniences, medical devices and the gear they so love, would not exist.

          Had scientists, chemists and inventors shared the doctrines of the Cargo Cult (Denyin'tologists), there would be no semiconductors, computer chips, LASERs, or Magnetic Resonance Imaging devices (MRIs).

                                         Solid State amps?

                                     OOPS (back to tubes)!

                                        Your Smart Phone?

                                        FA'GET ABOUT IT!

                                         Your car's GPS?

                                                NOPE!

    Then too: some may be willfully ignorant and just enjoy being contentious.

                        Others: obtuse, uneducated*, misinformed?

      *Typically, from what's been exhibited here: H.S. STEM, if that, would be a safe inference.

      Either way: the result, when the Cult begins its rhetoric, is a classic demo of the Dunning- Kruger Effect.

                                          But, I digress: 

       Bring up those pesky details, regarding the likes of QED, Dielectric Absorption, Poynting's theorem and possible application/effects, relative to frequency, that our musical signals are carried via photon or wave, outside the conductor and you're a KOOK?

         Again: the Cargo Cult can only understand anyone with an actual background, experience and education in Physics/QED, based on their beliefs, education, experience and biases

                                      Remember this?.

     One anecdote  that some may find interesting: their walks in the woods and how Feynman's father would encourage him to look beyond the fact that something in nature exists,  into WHY and HOW.

     It saddened him that while attending college, during a visit home and one of their walks: his dad asked what he was learning in college.

     At that moment, he realized: if he tried to explain what he was learning, there was no way his dad could understand.                               

                            It wasn't an insult or condescension.

                                                Just reality.

                              Oh well: let 'em go build a runway!

                                                    references:

https://en.wikipedia.org/wiki/Applications_of_quantum_mechanics#:~:text=Examples%20include%20lasers%2C%20electron%20microscopes,systems%2C%20computer%20and%20telecommunication%20devices.

https://www.forbes.com/sites/chadorzel/2015/08/13/what-has-quantum-mechanics-ever-done-for-us/?sh=37c459944046

https://uwaterloo.ca/institute-for-quantum-computing/quantum-101/quantum-applications-today

          But: I'm a kook, because I believe in the SCIENCE, from which all that sprang?

     https://www.smithsonianmag.com/science-nature/five-practical-uses-spooky-quantum-mechanics-180953494/

           Einstein got that last one wrong (Quantum Entanglement), BUT- I still wish he'd been alive, when the Hubble Telescope proved what he considered his, "greatest blunder" (his inability to bring symmetry to his field equation, without lambda).

  https://www.aps.org/publications/apsnews/200507/history.cfm#:~:text=Einstein's%20original%20equations%20had%20been,how%20the%20universe%20will%20end.                                            How about that?

Another example of a hypothesis/theory, with no way to MEASURE, what you're sure must be there, in some detectable way, or another.

                                               Just for fun:

https://www.scientificamerican.com/article/6-times-quantum-physics-blew-our-minds-in-2022/

                                            Happy listening!