The delta between the book value and the securities pricing is the estimated future profits. Now how exactly did you arrive at the conclusion that the future profits estimation is too high?
But, since we're now talking about overvalued securities:
https://www.npr.org/2021/05/05/993754418/planet-money-the-10...
The market returns are calculated over a fixed and usually short time period and are easy to calculate. Because the markets in question are expectations markets the prices move around a lot and hence the measured returns move around a lot.
Compare that with defining "returns on actual businesses" in a way which is both sensible (ie accurate) and has even a reasonable level of precision - it's impossible. For example, a commonly used and easy way to measure it is Return on Equity. Net Income / Book Value. Book Value is an accounting number based on the past. The "true" value put on an asset by investors is based on guesses about the future of the business and said business's ability to put cash in the pockets of the owners. Net Income misses important value changes - consider Intel, who have been making crazy decisions for years which allowed AMD back in the x86 server game. Intel don't have to report a "we did stupid things which will cost us billions in 10 years time" on their income statement for a given year. So, RoE isn't good and other similar numbers are similarly bad.
So, your statement about returns on securities should really say: "for the last few years, returns on securities appear to have exceeded the changes in value for the underlying businesses". To which a reasonable response is: "Yup, it happens sometimes".
I would argue that there is an increasing amount of evidence that statement has gone from "plausibly true" to "pretty obviously not the case, for many securities."
The underlying problem, regardless of the terminology or metrics being used to estimate value, seems to be that those with $10b in cash seem increasingly inclined to use it to speculate using various financial instruments, rather than e.g. building a manufacturing plant or a new housing development or apartment building. The growing size of the financial sector relative to the rest of the economy is the evidence I would put forward that "the returns on securities are exceeding the returns on actual business."