electric guitar grounding for safety
I think what's missing is an appreciation of why an electric guitar is the way it is.
The wiring of an electric guitar is basically UNCHANGED since the introduction of the iconic Les Paul and Tele/Stratocasters in the 50's.  So what you have is an instrument that's designed to work with the amplifiers of the day.  Virtually every electric guitar from every manufacturer today is wired basically the same way.
In 1955, the vast majority of power outlets did not have a 3-rd wire ground or even have one blade bigger than the other, so it was not only easy to get hot/neutral reversed, it was EXPECTED to happen 50% of the time.
To accommodate, a guitar amplifier chassis had a 'ground capacitor' switch such that the user could tie his instrument 'ground' (i.e. the plug/jack) to either of hot or neutral through a high-voltage capacitor.  The user would pick one of three positions (connect to either AC wire, or no connect at all) until the point of lowest hum was found.
This capacitor has since become known as the 'death cap', because a failure of it places live AC voltage on the strings.  (https://robrobinette.com/Death_Cap_and_Ground_Switch.htm)
It's just a crappy electrolytic, not a safety device, and such a scheme would never fly today.
Guitar amplifiers have had to keep up with changing UL standards etc.. so yes today you would find proper 3-prong plugs.  But people don't throw away old guitar amplifiers - Quite the opposite, they are coveted.
It would be super easy to design a 'perfect' guitar plug that was noise-free, high reliability, and safe. But that would be incompatible with the vast array of already existing gear.  Nobody would buy it and it'd be a market flop.
The thing is, guitar players are almost religious about keeping designs &quot;vintage&quot;.  That's why the Les Paul/Strat/etc  have been in continuous production nearly unchanged for 70 years.  I challenge anybody to find any example of such a long-lived design in any other field.
Guitarists are strange creatures --- Tweak the design, they won't want it.  So it's the market that DEMANDS that guitars remain wired the way they are even though EE's know it's &quot;wrong&quot;.