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.
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.