Cryptocurrencies are too much correlated to Bitcoin. If he plunges then all altcoins will follow the same path or even worse. For me, buying only Bitcoin is the best thing to do at this moment.
On the link below you have some plotted data:
https://cointimes.com.br/investment-diversification-in-cryptos-bad-idea/For example:
Correlation between Ethereum and Bitcoin is 0.82 which means a very strong correlation. In 2017 the same correlation was 0.41. For me, if you're diversifying in two types of assets that have the same correlation you're doing it wrong.
What do you think about it?
You had a point here, eth and btc are closely related in terms of buying and selling. But, you also need to take note of the functions of each type. How each of type of coin has been earned? ETH coverage is wider than BTC. Most of the ICO tokens are supported by ETH only.
Diversity would be good because each coin plays different functions.