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You could say that, sooner or later, all cryptos will decouple from fiat, because fiat value will spiral down. I'm talking just about the current context, in which a significant amount of STEEM suply, namely a third, is traded on other pairs than BTC / ETH. This is decoupling, since you can clearly see that tokens traded mostly in BTC / ETH are going up and down with them, whereas STEEM has a bigger inertia.

June '17, Jan '18 and recent small alt jump show heavy correlation. Im not sure I believe you :)