Possibly what you said could be true, but you also have to realize that the price of BTC can drop 100% from the highest price, then most other altcoins will also experience the same thing even though the decline will not be 100%, because altcoins will not be able to survive with good if BTC starts to decline by a very deep percentage.
correct, there's always a possibility that most of the altcoin in the market will follow after, wherein once bitcoin plunges. As the matter of fact I'm now facing on my monitor with four different graph and i noticed that most of the time when bitcoin and ethereum fluctuate some of my alts are showing the same pattern as well at the same time.. I dont know if you keep monitoring the price in CMC but to be honest when bitcoin is down i see that the market cap in CMC is red and most of the crypto currency are red also.. So i can say that they will follow with bitcoin if it fall back and struggling.