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Why would ALL cryptos correct? There are certainly a few cryptos which have real world utility. The prices of their respective tokens would only increase the greater the market share they encompass. So, it does matter, it would be pure ignorance if you say otherwise.

its obvious, they all move up when bitcoin goes up and vice versa. nothing goes up forever

I dont think you understand how this works. At all. The long term value of any asset depends on the amount of value it generates for an economy/society. Despite the fact that there might be short term corrections, coins can have a general uptrend over the long term.
The upside is very much infinite, while the downside is limited to 0.

agree, however right now, all CCs are following bitcoin until such time they decoupled from bitcoin for the reasons you mentioned.