Yes, it is already observed that the fall of the price of Bitcoin affects the prices of the altcoins. Bitcoin is the most famous, used cryptocurrency right now around the world, and it is normal that its volume and market affect the whole crypto market, that is why even when the BTC price increase we see that most altcoins go up too.
I don't think the fact that Bitcoin is the most famous is the reason why it's dominance is so great. IMO it's the fact that most coins/tokens pare paired with BTC and because a lot of those project doesn't produce any real product yet, is the reason why their price could be easily moved by BTC movement.
Most ICOs don't have the actual product now, still on test net or development phase or whatever, except for a few.
There were lots of platforms do exist though and we can see it on the top rankings but still most of the or all do tied up with BTC pairing.So if there's a fall on bitcoins price and
due to Bitcoin dominance is too big compared to combined percentage of altcoins then its just normal to see that the entire market would be heavily affected.
There might be some projects can stand up but they would still be dragged down.
