This is a misunderstanding of what "wealth" actually is for the capitalist class. You are imagining the dollar value as a means to purchase commodities. It makes sense if you think of money as a means of holding the value of labor. You're interaction with money is in earning a wage doing labor. You then use that money to purchase the things you require to survive. You use that money to get the products of other peoples labor. Money for you is a means of holding the value of your labor.

This is not the relationship with money that the capitalist class has. Money is not a result of their labor. It is a result of their extraction of value from the labor of others. They are not concerned with their ability to "afford" something. They are concerned with their ability to maintain power within the capitalist class.

The dollar value of their wealth is measured in the control within that class structure. The measure of their wealth is the measure of exploitation and influence they have over the rest of society.

So, yes, it's not dollar value trillion in a bank account. But that doesn't matter. At the degree of wealth we are talking about it doesn't matter if you use USD or bottlecaps; just so long as you're measuring it consistently to describe the power and influence that unit of measurement describes.

Saying "they aren't really a trillionaire" isn't really meaningful. Money is fake. We made it up. Society accepts this measurement as a measure of describing the fucked up distribution of resources. That's all this term is really describing.

Saying "they aren't really a trillionaire" is basically just saying "they don't really have this much control over us". When, yes, my every material metric they do.