I think there are no coins that work on the platform of Bitcoin, only some coins are created from the fork of this coin.
Bitcoin is the king of the cryptocurrency market so when it drops in price it creates a market effect that causes other coins to fall.
Well i suppose bitcoin source code was the main refrence for almost all altcoin even though it's not forked from original Bitcoin source code, For the price itself i agree with you, Bitcoin is the standard on the crypto market and when it's dump then everything will going to dump too expect Stablecoins, Well that just how the market works.