You're right. Having bitcoin in your portfolio, you can make great money. It is not necessary to have a complete portfolio of altcoins. Especially if you dont have experience in trading. Trade Bitcoin and you will be happy.
Experienced traders will always decorate their portfolios with several large and promising coins. They will never focus on just one coin, because they know, trading on one coin has very little chance of making a profit. However, if you fill a portfolio with several coins, the opportunity to get profits will be greater.