That time has not come yet but in future that will be the scenario. By large the sentiment of entire cryptocurrency is still driven by Bitcoin. So whenever there is a positive sentiment around bitcoin, the same is also reflected upon the altcoins and subsequently it goes through a buying spree. Similarly the reverse is the case whenever there is a negative sentiment.
But at the same time I must say that we are approaching an inflection point, where the new projects are coming up with robust solutions to the underlying problems of crypto and blockchain space and the various gray area is being covered up with solution. Some new generations cryptocurrencies are evolving as well. So we are approaching a point from where the real, value oriented and market centric solutions of cryptocurrency can only survive and others will become dust only. Because the real and concept based crypto will definitely survive even during the bear market and it will be driven by real utility value and not by hype. bitcoin will have its place always but the over dependency of altcoins upon bitcoin will fade away in next decade and then the key crypto assets will start to trade independently to each other.
There is also another important factor, that is mass adoption. Unless there is full mass adoption to crypto-economics the altcoin is not going to decouple from bitcoin. Because the mass adoption is something related to politico-generic things. Because even as on date the govt and the statutory body are standing on the other side of the crypto assets and challenging its existence and the crypto on this side is standing by having a generic identity and that is the reason why the coupling between the bitcoin and altcoin is so hard. The crypto space is still facing the politico-generic challenge from the traditional system and governance, . Once those things will settle out there will be real competition between crypto to crypto and at that time we will be able to see the cryptos to trade independently to each other.