I think you better have some bitcoin in your portfolio, I agree with you that altcoins are more profitable than bitcoin but the higher the return, the higher the risk so you should not invest all your money in altcoins.
More precisely half of the capital is invested in BTC for long term portfolio, I have bad experience have invested all capital in altcoins (besides top altcoins) for the purpose of double profit but everything was not as expected and even suffered high losses. Now my investment focus is only on BTC, ETH and BNB.