it's too risky to sell all altcoins and hold bitcoin, but I think the risk of holding a bitcoin is not as big as holding an altcoin. Bitcoin has proven to have great prices and great potential. maybe if now the altcoin held is an altcoin that might have a low price I don't think it's a problem to sell altcoins and buy bitcoin.
Actually it's not too risky if we have considered it very well. But if I become an OP, I might break my money into three parts to buy bitcoin, bitcoin cash, and BNB. I also used all my money for bitcoin, and at that time it was fortunate enough to go up in price. Altcoin is influenced by bitcoin and when bitcoin goes down the altcoin will also go down, so it's the same if you hold bitcoin or some altcoin because the price will go down too.