A straigh up marinade will offer little benefit for the overall brisket. It jsut won't penetrate enough to flavor the entire brisket. Injecting will achieve that end, although, it is then about the time and composition of the marinade. I can see this working for home cooking. I am not sure there is enough time at a comp for marinading to work.
BTW...I have cooked and eaten my fair share of competition brisket, and some of it is darned fine. The pot roast thing is a myth.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"I'm Armenian...perhaps...but then again...maybe not..."