I think that public companies can reveal true market value quicker than private investments.
For example, VCs invest in company xyz at a valuation of $100m, they don't actually know if that valuation is "real" until the company sells. Until then, it's made up numbers. That gap between investment and sell date might be 5-10 years and until then then there's no market proving of that valuation. We've seen it time and time again that private companies can exist with no revenue or at least no profit for years or until their private fund runs dry, but can still claim a "valuation" in huge numbers, even while the market provable "value" of the company is $0.
Public stock markets tend to suss out valuation much quicker, a company might be "valued" on the market with a market cap of $100m, but miss a couple quarters or some big sales and stock holders will dump and run and the market cap can drop quickly over even a matter of days or weeks. Public investors eventually start to want the fundamentals of their companies to be good even if they start as fantasies. Reportable revenue, eventual profit (or continued revenue growth that's quickly convertible to profit in the even of market saturation)...eventually these things all have to exist, and I'd wager that an analysis of stock market prices on a company over the long run has a strong correlation to these fundamentals. I can't go and buy 1 share of Tesla at $500 and suddenly claim the company is "valued" at $60b.
But you can do that with private companies because of the information asymmetry available to private companies. There's all kinds of wonderful ways to game "valuation", but that's fundamentally different than market "value".
There's an idea that publicly traded, but unprofitable, fast-growth companies, like Tesla, with big inflated stock prices are the same as overvalued privately funded companies, but there's some fundamental differences in those valuations. If Tesla's revenue growth curve turned downwards next quarter or two, their stock price would plummet and their valuation/marketcap would arithmetic its way downward as a consequence. But a private company's "valuation" would stay the same until the next funding round/corporate sales activity, a lag time that could be years away. Thus a private valuation is more likely to be divorced from any business fundamentals than a public one, and that's simply because private company valuations are more closely tied to investor activity not business activity.