On a UCAS form extracurricular stuff is (or should be) put in context in terms of how it is relevant to the student's application for their subject choices. It is part of their written personal statement that allows them to show how their interests tie in with their subject choices and what they have learned about their subject from them.
That's an entirely different scenario to you as an employer receiving a bunch of CVs with no written application. You're comparing apples with oranges.
That being said, I'd like to think that as an employer, you'd be able to think more flexibly and consider what traits and qualities people who had applied themselves to doing these activities might be able to bring to your organisation. Writing off quite significant activities as 'middle class' and 'completely indistinguishable' is rather harsh. Achieving a Grade 6 in a musical instrument is not easy. It requires a huge amount of dedicated study and practice, and the passing of the theory exam, too, which is also challenging academically. Do you know how bloody difficult it is to get a D of E Gold? It's only achieved by about a tenth of the students who get a Bronze, because it's incredibly challenging. The organisation provides financial support to those unable to pay - so it's not 'elitist' or 'middle class' - a good proportion of participants come from underprivileged backgrounds. And yes, ok, fine, it does cost a lot of money to go abroad and dig wells on your gap year - but at least these kids are doing something for others, and had the bravery to go out of their comfort zone, try something new, and hopefully learn from the experience. Most young people don't take a gap year, and don't volunteer in any capacity, regardless of who they are or what background they come from, so it's still something to be commended. There's no need to be so judgemental about it.
I'm disappointed that someone who appreciates the beauty of Olga Tokarczuk's writing can be so closed minded. Behind all of those achievements you've just written off as being pointless is a huge amount of hard work for those individual young people, regardless of what family background they have.