I don't see how his statement requires one to assume wealth inequality (WI) is an important metric. He's just saying one consequence of WI is what we're seeing.
And the consequences of aren't important? Let us recall he claimed a pretty big thing:
When you let the rich have all the money they've got very little left to spend it on besides conquest.
He also claimed that things were different for the last century due to a "rapid onset of technology".
What's so odd about it? If something is seen as bad, there is no such thing as a "desirable" level it. Do you have a "desirable" level of turd in your sandwich?
Everyone who eats sandwiches implicitly has a desirable level of turd in their sandwich. Small enough that they never know it's there by taste, smell, illness, etc.
But wealth inequality doesn't even come close to the disagreeability of the turd-free sandwich. Virtually everyone agrees that someone who tries should have better ability to accumulate wealth than someone who doesn't try. That leads to an inequality which near universally agreed upon. The connotation of wealth "inequality" deceptively implies that the ideal of wealth "equality" is better, but few actually buy into that unlike the ideal of the turd-free sandwich.
Actually, rich people would be LESS successful under such conditions. All those poor people can't afford to buy the luxury stuff that richer people would buy, limiting what new businesses the rich people can create, which means less new jobs for poor people, which creates a downward spiral.
Utter fantasy. We only need to look at the developed world to see that you aren't even remotely accurate. Rich people got richer because capital, the primary sort of wealth of rich people, continues to climb relative to the wealth gathering value of labor. It'd be nice, for example, if my wages had tracked the NASDAQ Composition, for example. My minimum wage of $3.65 per hour in 1987 would be roughly $50 per hour today.
You're also using a particularly erroneous version of the demand-driven model of the economy. Somehow it's really important that developed world people have a weak inflation-adjusted increase in their wages, but not important that the far more numerous developing world workers have massive increases after inflation in their wages.
But even if we ignore that, demand is not just driven by consumers. It's also driven by employers who always get short shrift with this particular model. I consider that a major error of the model just on its own.
If left alone, this would eventually decreased wealth inequality (e.g weaker businesses close down, the rich become not so rich anymore). So the fact that it has shifted so little is a sign that the elites are propping up the system, preventing the market from correcting itself.
And it has in the developing world. But it hasn't in the developed world. The excuses are numerous, but I think I nailed it with global labor competition.