The people who are still holding, or the people who sold at its height, to people who were hoping for more? If the former then they haven't gained anything yet, if the latter, that's the greater fools.
The top so far. I have no idea about the future. Regardless, when do people sell? When it's at the top? When is that? If it's going up shouldn't you continue to hold? And should you sell when it drops? You haven't. So what's your line in the sand? Should new people be buying in? When should they stop? And then who are you going to sell your coin to? The greater fool.
Comparing bitcoins volatility to fiat is ridiculous but regardless, you haven't made any actual guaranteed monetary gains until you sell.
Ok, sure, avoid the other questions, but to be clear, paying for something with bitcoin is the same as selling it, you're just pretending that there isn't a conversion to fiat somewhere in the chain.
When I buy a house in Dubai with bitcoin, there is no fiat involved. I receive the house, they receive the bitcoin. Simple. You could call this selling your bitcoin, but in the same sense you could say selling your fiat.
You seem to think that fiat currency is somehow a base unit like meters. But it isn't. Maybe you have noticed the inflation all over the world recently, some countries more than others. Like I said before, all asset classes have risks. The statement "cashing out" makes no sense to me. I have various stores of my value. Fiat, crypto, companies, real estate, jewelry, bullets, ...