Being a ball chair is far more demanding ..... than a few hours in a cafe on a Saturday
I suggest you try doing an 8 hour shift in a supermarket, bar, cafe, restaurant etc. so you can see exactly how wrong you are
Dealing with the public, as a 16 to 20 year old, especially when they're complaining/being aggressive etc. is demanding.
Having to start a shift at 6am or not finish until midnight, and fit your shifts around your studies/sports commitments is demanding.
Doing menial, repetitive work is demanding.
But it teaches our DC a lot of experiences that, in most careers, are beneficial.
Yes, being a ball chair is hard work (I did it myself 30 years ago) but it's something you volunteer to do (not something you need to do to get money), the people you're working with are generally compliant, and you're normally the customer when it comes to negotiations etc, not the supplier. Plus it's usually a 6 month gig at the very most.