People need to stop believing in this TOP 10 fairy tale. if an altcoin suffers a lot of pump and dump it will surely be in this top 10 even though it is shitcoin, so this top 10 should not be something of a metric to say that an altcoin is good or no, on the matter of diversifying, if someone buys a lot of cryptocurrencies that person is not diversifying the investment, that person is just taking more risk of losing money. to diversify would be to have a cryptocurrency, to have other assets like gold and business in the real world
I agree with you that there must be variation in purchases but in that case you must think about which particular asset need to buy. I think if anyone invest in top 5 coins from top 10, the chances of losing are relatively low. In this case, there is a high possibility of increasing the price. one or two coins may be fallen in risk, but it is not possible for top five to collapse together.