The article misses the purpose of a measure like market cap. It isn't to state the value of a single tradable unit like a share (which the article seems to think it is meant to represent), but rather it answers the question "How big is the company economically" and helps compare companies in ways that price alone can't.

Market cap correlates with risk profiles. It informs index construction (like the S&P 500). It is often used by investors in capital allocation and portfolio weighting decisions. It is a key input in valuation (but not the valuation itself). It is used in M&A and strategic decisions.

The way to think about it is:

stock price = cost of one slice

market cap = cost of the whole pizza