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).
If I understood you right, you mean that Bitcoin is the equivalent of Dollar in the crypto currencies world ? If this is your question, then yes for sure Bitcoin is the oldest crypto currency and the most successful and valuable one right now. All the other altcoins get influenced by the Bitcoin's market and price, and it is needed to trade most diogiatl currencies.