But fact is, there are many cases where one investor tries to buy the whole company, the investor has to pay a premium over what the market currently values it

But fact is, there are many cases where one investor tries to buy the whole company, the investor has to pay a premium over what the market currently values it at (Musk buying Twitter for example). So the current market price is a good approximation for what its real value is. Unless you think you know better than what our modern finance theory says, then I don't think your point is valid at all.