If we compare the crypto assets market to the stocks markets in general, can Bitcoin be considerated as the equivalent of the dollar?
In the stock exchage we buy shares with dollars.
In the cryptocurrencies exchanges we buy tokens or coins with bitcoins(and other cryptocurrencies, Litecoins, etc).
There is no comparison between bitcoin and dollar as such . Dollar is just a currency restricted to one country and bitcoin is free of such things and is decentralized and independent of government . Bitcoin is also very dynamic and can be converted from or into any other digital currency . Bitcoin and dollars are only compared for price comparisons in order to simplify the people about the current price of bitcoin as they are more interested to know the price in dollars since bitcoin is not very much accepted by the governments.