BTC price has huge impact on the price of other cryptos at least for now. When BTC price rises almost all altcoins price will also rise and vice versa. Being the first and well known cryptocurrency makes BTC price have a significant effect on price movement of the entire market. This has been the case since the beginning of cryptocurrency market.
This price dependence may be reduced or even disappear in the future but there's no guarantee. It's possible that Steem price can moon without influence from BTC price but I don't think that will happen in foreseeable future with BTC market dominance still around ~50% right now. So yeah, BTC price is still important for Steem users in my opinion until the price dependence disappears.