I think that this is true, but at the etherium it is not much manifested. At the moment, all the coins have fallen, but it's hard to say whether this is due to bitcoins or whether the entire market is falling.
No coin is dependent on bitcoin price, it has an independent market and community making it grow and eventually makes the price at good standing. But Bitcoin is a big factor on the changes of the altcoin values since it is the primary pairing coin on most exchange. In addition, it is also one of the best established coin that is available in the market. It's community also are the same community that is involved in other altcoins.
The altcoin market is directly tied to BTC and fiat. BTC is a major trading pair as you said and an entry point. If you look at the price of Bitcoin, it directly affects the market of every coin, there's no question.