Your example is collusion/price fixing, and is very illegal. I think no matter what is being traded in most jurisdictions. https://en.wikipedia.org/wiki/Price_

Your example is collusion/price fixing, and is very illegal. I think no matter what is being traded in most jurisdictions. https://en.wikipedia.org/wiki/Price_fixing https://en.wikipedia.org/wiki/Price_fixing If you remove the collusion, then market cap appears to me to be a fair valuation. If there is a shock to the system and everyone wants to immediately sell (despite previously wanting to hold), I would argue that to be a sudden change in the valuation.