Let's say that the market cap of a coin is the measure of the trust that people collectively have towards the coin. If coin X costs $1, and people A, B, C, and D own it 4, 3, 2, and 1 units respectively, the market cap equals $10. This much money the people are willing to trust to be held in this coin.
Is the market cap a variable worth considering?
Person Z, creator of the X coin, mined 1 trillion coins in the first hour after creating the currency. After giving out those 10 coins to A, B, C, and D for free, he sold one coin to himself for 1$. Presto, the market cap is 1 trillion $, and his friends's hoards are worth 10$...
Market cap is a meaningful concept for items whose market liquidity is close to the total issuance. If all owners of Apple stock (or even gold) were somehow forced to sell all their holdings on market within one year, their total revenue would be fairly close to the market cap. That is not true for cryptocurrencies, not even for bitcoin.
Perhaps you meant to say that A, B, C, and D bought their coins at 1$? In that case one should exclude from the "market cap" any large hoards acquired well below market price? Or replace market cap by total invested capital (sum of the dollar amounts that current owners paid for their coins, plus interest perhaps)?
EDIT: I take back the "even gold". I have no idea of what woudl happen to gold price in that scenario.