When BTC goes up and downs alts are bleeding,while btc stabilize the alts are pumping thats my own observation,thats the reason why the BTC is a killing machine for alts.
it is difficult if a coin that has long been trusted can be defeated by altcoin and that has happened to bitcoin as far as I know bitcoin is the parent of many coins and applies to ethereum and if the price of bitcoin goes down then altcoin will come down, it will be difficult for altcoins to shift the price and position of bitcoin.
Bitcoin is the first coin, ethereum is totally different project, with different purpose and bitcoin and ethereum are not competitors. We can compare them in terms of price, bitcoin is much more expensive than ethereum is and maybe that will stay like that for a long time, maybe ethereum can come closer, time will tell. There`s a lot of things going on on ethereum platform and nobody should underestimate that.