The decisions is all yours, You can choose altcoin or bitcoin etc., and no one will stop you. In crypto we have different sight and different strategy if you saw that there is an advantage on investing in altcoins then be it grab it for good because at the end you will be the one to earn or suffer if you do right or wrong decision.
Someone who says that he would go full altcoins, let them do what they want.
We've said enough that it's better to have bitcoin as we also hold altcoins. Having no bitcoin on your portfolio will make it like it's not safe for most of the possible dump that can ever happen.
He should've realized soon that alts are very volatile.