It was always going to be Garrett's offense in 2019, and yes this would be collaborative from the standpoint that many OCs do not enjoy complete autonomy. I could see how install and game-planning responsibilities would be shared. Hell, even during the course of a game, discussions over what to run are happening across the league. Boy Wonder was never charged with redesigning anything.
That being the case, the matter of deploying wrinkles, tweaking, showing different looks may very likely fall under Moore's purview. At the very least, he will have some influence here as well as adjustments on the fly. Or that an idea may be floated by the new OC - the sort of thing not considered before. I don't think an overhaul is required. Perhaps fresh eyes and a new application of the existing scheme will do.
This is not to suggest this offense is set to take off. I do agree that a head coach on a seat as hot as Garrett's may be quick to step in if the offense sputters. That's only logical. This will make for interesting talking points for the fans and media, but, as always, moving the ball and scoring points boils down to execution.
As for these comments from Garrett, I would only say he is responding in the way most head coaches think, except that his programming *once again* failed to execute the logic that prevents him from droning over the obvious. Might there be a hint of defensiveness from a guy going into the final year of his contract when asked repeatedly about a first-year fresh-out-of-the box coordinator? Sure. But mostly, I just think of this as less of a "message" and more of the Garrett automation in progress.