And when the value of bitcoin falls, the value of other cryptocurrencies also fall, meaning that the impact of Bitcoin is strong regardless of its price in the market.
Not most of the time, there are some altcoin that continues to go up even when bitcoin is going down during altseason but yes I can agree that the impact of bitcoin is strong given that the down times can be an indicator for altseason.
The movements of altcoins are not exactly as the ones you can find in bitcoin, but they are extremely similar, if you take a look at the moment when we shift from a bull market to a bear market you will see that very few altcoins will still go up in value one month after bitcoin began to go down, the majority react very quickly to the influence of bitcoin and they go down just a few days or weeks after bitcoin has began to do so, demonstrating once again the high correlation that bitcoin and altcoins have.