It's not like there's a fixed number of naturally occurring megayachts around and the $500m price is a fiction that isn't fungible to be used on other things

It doesn't seem related to the "you have a trillion dollars on paper but that's mostly fiction" topic. The $500m yacht has been materialized to "atoms" and isn't on paper anymore.

Maybe you’re trying to say if they actually liquidated their wealth to spend any sufficient fraction their paper wealth would disappear but that’s the point of pulling out the value without liquidating.

Put it another way: I'd also have little to worry about if I could borrow 200k from the bank for a project. That'd basically be used to pay rent and get minimal equipment I'd never be approved for it, though.