No one will ever ask buffet to diversify. He is a great stock picker and his net worth speaks for it. Diversification is a tool for the less financially savvy investors. People who do not have time to understand market cycles or whether to invest in stocks or bonds or real-estate - diversification works well for them. Diversification after all comes from the work of a Nobel laureate. It's not retarded.

Diversification in crypto markets is not really possible. Crypto, in that regard, are like stocks. All extremely correlated and everything has a beta > 1 wrt Bitcoin. i think its really a case of risk appetite when it comes to cryptos, Bitcoin is the US treasury bonds of crypto world, top 10 is low risk, anything above 100 million dollar market cap medium risk, and beyond that - risk territory "balls of steel".