I prefer to compare Wilshire to metrics of the value of Wilshire, or S&P to metrics of the value of S&P 500, etc.
But still, it's not so bad. The fraction of US companies that are publicly listed doesn't change THAT much though time.

The most interesting thing I found from that article is how close relatively recent valuation levels were to their crazy 1999/2000 peak.
Those are levels I never expected to see again.

Using the Wilshire quarterly numbers for market cap (quarter average) as a percentage of GDP:

Average since 1970: 82.8%
2000 peak: 136.9%
2008 low: 56.6%
2022 peak (Q1): 195.3%
End of 2022 (Q4): 146.7%

So recent levels (at least for the last 4 years) are not just close to the 2000 peak, they are all well above that crazy 2000 peak. The Wilkshire 5000 is down about 15% from its all-time peak at the end of October, 2021, and GDP is up a bit, but that's not enough to bring the most recent ratio back down to the 2000 peak.

This is not at all in tune with what many people are saying about 'low share prices' since the recent correction. We are still more than 60% higher than the 50-year average. And even counting only the years since 1995, the average of the last 25 years is still way below where we are now.

dtb