I think that diversification is the key to success. It is better not to invest all your funds in one coin, even if it is bitcoin.
Yes, we should not focus on one asset no matter how good it is, because everything is always risky, and diversification is essential. But I want to tell you that once you have invested in bitcoin, investing in altcoins is not considered diversification. All altcoins depend on bitcoin, what if bitcoin crashes? Surely the entire cryptocurrency market will disappear. So, when it comes to diversification, we should invest in non-crypto-related assets like stocks, gold... not in altcoins.