You're not wrong, but the weakness you point out isn't a new concept.

Market cap is, at best, a rough valuation of the company. It has many confounding variables of which liquidity can be one of them. That's part of why investment analysts put out price targets for companies. The counterpoint is that market price is driven by what people are actually paying.

One of the major challenges with valuation is settling on a methodology overall. There are many ways, appropriate and not, to value a company. Many will have different estimates for value. There are also factors, like control premium, that start to become relevant when you try to completely acquire a company.

One of the benefits of an open and liquid market is that future availability of locked shares can be priced in early. We all get the benefit of consensus information.