Have you ever gotten hit by a Z-Move, or a Dynamax/Gigantamax move? If so, what are those like?
I have not. Z-Moves can only be performed by a Trainer-owned Pokemon and finding a trainer and Pokemon that are willing to use a move on me, especially without holding back a great deal, would be difficult. Besides this, there are some legal issues with the matter of ordering a Pokemon to attack someone, even with the target's permission.
Wild dynamax is rare and you cannot get into a battle with one without some idea of what you're getting into, dynamax bands aren't given to every person. Some things I do not think need to be answered, anyway.
The pain index serves to encourage people to be safe with how they engage with wild Pokemon and battles, since just saying 'this is dangerous' doesn't do much to dissuade because our familiarity with Pokemon makes people downplay the danger they can pose if you act stupidly, especially children and teens. Having exactly what will happen if any given move hits you written out in detail can serve to get it to actually click. Kids don't like being told to do or not do something 'because I said so', they want a reason. I provide the reason.
However if you somehow manage to not recognize the danger of a Rampaging powered up Pokemon the size of a skyscraper, I think you are entitled to the Darwin Award you're about to earn and nothing I could possible write would stop that.