Market cap is more like a popularity contest than any real promise of worth. With thousands of altcoins to pick from, most are empty promises or downright frauds and even if a buncha folks toss money at something, whos to say it will pan out. Ill give you that some altcoins might make good, but big communities dont always mean true usefulness in the real world. PEPE, for example? Come on. You cant seriously think that meme coin is worth over $5 billion.
You are absolutely correct that market capitalization is not indicator of intrinsic value, utility or promise for future for any digital asset, instead it is often seen as measure of popularity or to some extent reflects the market sentiment. This sentiment in my opinion is important because markets often operate on emotions and herd mentality, with fundamentals analysis often coming later. Meme coins are good examples' in this regard. The price of meme coins like PEPE and others driven by market sentiment despite lacking any real life use case.