First you need to decide what kind of coin retention period you are talking about. The practice and experience of most traders indicates that the portfolio for the long term may contain only one name of the coin - this is bitcoin. As for alts, now its probably the time to go against the temptation to acquire altcoins for a long retention period. Today its worth checking every source of information. There are many biases. The reward is most likely not worth the risk.
I agree with you. Investing in Bitcoin looks much more reliable than investing in altcoins. But I think its of great importance at what price you buy your Bitcoins.