The whole crypto will always act as one. It is not because of individual characteristics of each coin but it is because of human behavior. We humans tend to group things together so that in the markets, industries fall and rise together.
Good point from that part as the hole industry was supported by investors and there's always people who will keep bringing new ideas but will also
take part of the original concept. Alts will depend from bitcoin and bitcoin investors will look after alts to bring something good from their investment.
It is true that when the market is going up similar assets have a tendency to move together but this tendency is even greater in the market of cryptocurrencies because as we know a substantial amount of the projects are just copies of bitcoin which means that they are heavily dependent on the behaviour of bitcoin for their progress.
And that is a problem because everything depends on the fate of one single coin and when bitcoin is not doing well then the whole market is not doing well.