If bitcoin will hit $6000 then it will probably end up with $5800 or $5900 ethereum can hit $400 but that does not matter there will be bounce for me.
Normally cryptocurrencies price should not be correlated to each other but most of the time, it just follows the bitcoin price, and I agree with you if BTC will drop under $6000, ethereum price will drop under $400 unfortunately.
We cant say that the market value of any other crypto coin is dependent on the market value of bitcoin completely but there is some effect of the market value of the bitcoin on rest all other crypto coins and the reason behind it is that bitcoin is the backbone of this entire crypto market. ETH has a sting potential to grow but for now, things are not that much good and that holding of ETH is the best thing to deal with such kind of situation.