In that case, the intelligence/suspicion was wrong, processes bad, and the death was tragic. It wasn't like they went out to kill a man they knew was innocent, at least not for the officers on the ground.
Hindsight is a wonderful thing, but it is always 20/20, the death of JCMD was tragic, and should have (and has) led to changes in the processes, but it was an operational error, at a time of both hightened security and pretty severe paranoia (happening only a day after a failed multiple suicide bombing attempt where one of the bombers came from the same flat/building JCMD had been seen leaving).
The met were held responsible, incidentally, your link acknowledges this.
I would hardly say they were held responsible. They got away with paying £100,000, only after fighting to cover up their wrong doing. No charges were ever made against the people who sought to cover up the wrong doing. They got a slap on the wrist for murdering an innocent man and trying to cover it up.