This is not true. Bitcoin is more stable than most altcoins. When the market is in a long-term bear market, Bitcoin's decline is much smaller than that of altcoins. You can check that the market has found that most altcoins have lost more than 90% of the value.
If we check the earlier market, you will find that the current price of Bitcoin is still much higher than the price a few years ago, but altcoins are not necessarily, many are dead.