Have you tried using it? If not how can you say if it is useful or not? Plenty of people use Bitcoin to buy charlotte's web for their epileptic daughter and other things, so clearly it's useful for them.This.
And it's not really useful even in black market, since the whole bitcoin blockchain is transparent, nothing is private.
In essence bitcoin is not fungible like cash, moreso the coins can be tainted. If a pseydonumous address has been used to buy drugs, you only need to look at the blockchain and see that those coins were used in illicit activity.
Bitcoin is not transparent, if it was drug dealers would not use it. It may not be anonymous but it can become anonymous enough using mixing services that all black market sites use. Though some people prefer to use Monero just to be safe.
In practice it's really hard to know if the bitcoins you get for that coffee you sold at your cafe was tainted or not and the shop owner doesn't really care as long as coinbase will convert it to dollar if he wants. And coinbase will do this. For very large transactions such as a Mexican cartel getting paid for the shipment of cocaine to California the DEA might actually care to trace it if they can, but not for every random transaction on the blockchain...