Stosh, I disagree that a small group of eight functions the same as a larger group made up of groups of eight, for exactly the reason I added Patrol Advisors when I was SM. One person, even if he, or she, is a SM, is still one person with a finite amount of time. A SM with seventy scouts in his charge would not even have enough time to handle all his SMC, much less do anything else. The system I describe gives each patrol access to an adult leader, who is only tasked with being available to that patrol leader, and handling SMC for his patrol.
As far s adding another adult to interfere, and take over, not if your adults are correctly trained. After my tem as SM ended I was made a Patrol Advisor; I've never observed a patrol meeting, never camped directly with my patrol, only ate with my patrol if invited, never addressed the patrol as a group (although I've been asked to by the PL), never touched apiece of the patrols gear, and never gave the PL a directive ... none of those are my job. I have conducted many SMC's, listed to the PL mull over issues (asking a question here and there), I've issued blue cards, found merit badge councilors, and listened to many camp stories ... I've also been the but of a skit or two.
In a large troop the SM can't do it all, he has to delegate. A patrol advisor acts like a mini SM for one patrol.