Irrelevant. There is a large concert hall close to my home, complete with pipe organ. The hall is available for rent, which does not exclude religious organizations. If a Catholic parish would rent the hall for a large event, which would include a mass, it would be a foregone conclusion that the Wurlitzer would be used, even though it is used for secular purposes. The point being argued is that any instrument by its very nature is holier than another, which is silly.
The claim isn’t that one instrument is innately holier than another, which would indeed be silly. There are essentially two considerations.
One is whether the characteristics of the instrument, or style of music, supports or detracts from what is going on at the Eucharist. So if the musical instrument is being used to lead the people in singing, but is too quiet to be heard, or so loud it overwhelms the singing, that would not be appropriate or useful. This can vary depending on the setting - what works in a big cathedral might not work in a hospital chapel.
The other aspect is cultural associations. Imagine for example that in a particular culture a certain instrument is used in orgiastic religious ceremonies involving human sacrifice. Given the associations, it might be best for a Christian church of any kind to avoid that instrument in their worship.
That is an extreme example, but not unrealistic. Sometimes in the past reasons like that were indeed cause for disallowing some instruments. In the West, with a culture that has been broadly Christian for a long time, examples aren’t usually quite so clear.
So what do they want to avoid in Mass these days as far as cultural context goes? Instruments and music that will seem like a concert. Ones that suggest excessive emotionalism. Anything that is really associated with a trend that is against what Catholicism believes.
As for organs, guitars, and pianos. Well, I think people do need to remember that these things aren’t set in stone, as the organ was once a culturally inappropriate instrument in the Church. And the purest example of music for the Mass remains the human voice praying the liturgy in plainchant or simple polyphony. But there is a long association of organ music with religious services which is a significant advantage to that instrument, there is lots of excellent music written for it, and it works well for leading singing and has an almost vocal quality. (It can, of course, be played badly, or well but in a performance like way that overwhelms the liturgy.)
Guitar and piano - well, to be honest I think classical guitar can work well for liturgy in a more intimate setting as can piano. Guitar doesn’t always work as well for leading singers in plainchant of the liturgy IMO, and I would say there is, so far, less good religious music written for both, or perhaps it’s just more bad music for both. And they don’t have quite the same history of religious association. Which isn’t to say they couldn’t acquire it as the organ has done. At one time these were both really associated with things like music halls, but I would say that is less so now.
Electric guitar like in a rock band is another thing, I don’t think it or other rock music (which I like) works well in a Mass. It tends to seem concert-like, it can be too emotional, it is often distracting from the liturgy, and for too many people it’s association is sex drugs etc.
But none of this means that the instruments themselves are more or less holy. And it is clear that these kinds of considerations must be flexible depending on place and time.