I'm not sure if I'm following this example. A 500M Yacht concretely uses a large amount of materials/engineers/building expertise, right? It's not the exact same skills as building apartments but it is concrete "atoms" in terms of materials, engineering, sweat labor, fuel. Those resources could be used on apartments.
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.