>Rough (not absolute) wealth equality is a goal in and of itself we want a capitalist economic system to function.
No, it's not. Capitalism has nothing to do with equality. We can have extreme inequality as long as the workers actually get enough to satisfy them. That of course depends on many things like their productivity, supply and demand for labor, and preventing monopolistic abuses by corporations and labor.
>Capitalism only efficiently allocates resources if the market value of a good or service closely approximatatoon its "true" value to society. And that ceases to be the case when wealth is very unevenly spread.
Wealth inequality has nothing to do with market efficiency. Every person in the market makes decisions according to their own estimations of what the true value of a thing is. That's basically a democratized hive mind at work. If any individual spots a market inefficiency, they can try to exploit it, and in so doing increase overall satisfaction of market participants. This distinguishes capitalism from other systems like communism, which rely on a small number of central planners to make necessarily imperfect decisions for everyone based on limited understanding of the entire economy and all its participants.