One could argue that it is preferable to serial killers.
Serial killers meticulously plan and often torture their victims extensively and many of their victims families never get closure because nothing gets tied back to the killer.
Mass gunman attacks, for example, kill orders of magnitude faster with much less pain for many of their victims, the perpetrator isn’t active for a long period of time, and the families get closure.
Of two severely fucked up scenarios that happen, it seems that one is worse.