To understand the difference between bitcoin and alternative coins, you need to familiarize yourself with the history of their occurrence. I would advise you to read the book "Digital Gold: Bitcoin and the Inside Story of the Misfits and Millionaires Trying to Reinvent Money". In which the history of bitcoin is described in great detail and how it became the main cryptocurrency.
It did not become the main cryptocurrency,,, it was the very first one, and from there was the main and today still is the main one. Major altcoins are also seeing a lot of use, the most is Ethereum, particularly because of their dapps and all their ETH-based tokens, but Bitcoin is still the only one that really sees major use (spending, buying) besides trading. There is no battle for BTC, other alts might see it as a fight or even war, but BTC stands on its own.