Exactly. If it was Trump and quite literally any other Democrat candidate, having the right plan in preparation in place could easily swing the debate either way. However, as you said what we saw had nothing to do with if he had 1 days of rehearsal/prep or eight days. It was the tail sign that whatever drug cocktail, medication, therapy, etc. They have been using to keep him remotely. Cognizant is no longer working unless it is in a highly scripted environment.
I was pleased to see Trump so restrained during the debate, but I do think it was a calculated plan to just "let Joe be Joe" and become his own worst enemy. Trump was wise to sit back and only speak when it was his turn.
I doubt that Trump would have been as passive if another person were debating him that night, so people shouldn't assume that they would have gotten the Biden "Trump." They would have gotten the "Let Trump be Trump" Trump.
-PJ