I didn't read the study...just your summary.
But, my reaction is 'really???'
I have only had prescribed opiates twice in my life.... once was Tylenol 3 after dental work, the other for kidney stone pain....both times, the effectiveness bordered on spectacular, in my mind....near 100% pain relief with little side effects beyond drowsiness. Now, this is extremely small sample size, but I think different, subjective pain levels, from different causes in different people makes such studies extremely problematic for useful extrapolations or conclusions. Even if you buy into a study 100%, you can't deny that certain opiates still might be right answer for certain people in certain controlled situations