No doubt that BTC is still used on deep/dark web, but by some analyzes less than the previous years. One of the main reasons for the reduction of use is high volatility and maybe something even more important and that is less anonymity than before. Some security agencies like NSA are work for years on idetnification methods to track and identified BTC users ( Snowden provide evidence for that), so some other more anonymous coins take over the part of that market. More anonymity and low fees, this is something users ask these days.