I agree that income and (current) wealth are often fungible. The main reason I think wealth is usually reported because real income figures are hard to come by. If we want to look at the extreme end, current property and not income is the only option.

But, I think wealth (above definition) may be important as a stand alone. Many of the political implications of wealth disparity have more to do with current wealth than income, for example.

I do think you have a point though, as I said. Some wealth disparity is a matter of age, for example. But the disparities we have and those we project are very large. They may overstate disparities in income and consumption taken alone, but I don't think it's more clear headed to dismiss them outright. They do indicate a real and growing disparity.