It is not necessary to change Bitcoin to alts, it is always profitable to keep Bitcoin in your wallet, and then, if there is money, you can choose and invest in alts.
That's right, it's better to save your 1 bitcoin than break it up with several altcoins, because the increase in bitcoin is greater than altcoin and altcoin takes a long time the price goes up, if you want to buy altcoin it's better to use other funds
It is always necessary not to put all the money in 1 coin. So, I will also keep 50 - 60% in bitcoin and with remaining could invest in the other altcoins and a certain part may keep it for the new project which I may like, or it is worth investing in it. This would depend upon individual choice as some may want to buy altcoins, some would invest in only bitcoin etc.