I contend that they use multiple approaches. Yours is likely one of them.
But the one I now believe is most used is that most of the killing is done by a trained team (kind of a SWAT type assassination team) and the person groomed by the therapist is just there to take the blame.
Once the designated patsy is arrested - voila! - no need to search for the SWAT team. Because who would suspect such a thing? We all “know” that these shootings are done by crazy people, right?
One small bit of behavioral “evidence” is this: Have you noticed that in the cases where the “perp” is taken alive he always seems bewildered and disoriented? Doesn’t it seem odd that someone would be an efficient killer executing a well-planned attack one moment and then suddenly turn into a confused person who is dazed and bewildered?
Your analysis is I believe superior. Las Vegas seems to have clearly been more than one shooter from all the evidence. My research of the Charlottesville films seems to point to James Alex Fields having been a possible patsy or at least the false flag planners there having a lot of people there who looked just like him, as with Oswald way back when.