"Market cap" is a pretty dodgy figure to begin with, especially to compare things with very different liquidity.  But in the presence of substantial premines ETH or ultramassive premines like XRP, it's just an outright joke.

I could create some worthless joke coin with 100 septillion premined coins, sell one to you for a dollar and claim to have more market cap than not just all cryptocurrencies combined but all assets in the solar system.

Cryptocurrency marketcap trackers originally hard excluded premined coins, but eventually the bribery won out.

As it is, it's all about suckering people into turning the issuers into billionaires.