Just on this again. As coaches McVay and Shanahan seem to think they need to be ahead of the game as and second guess things. It's like "Sure it worked against the Niners last week but the Bears are gonna see this coming so let's keep them guessing". Not to sound like a jerk but it's almost like they've put so much time into their massive playbooks that they would hate it if they only ended up needing 1/4 of those plays.
The benefit of playing something like 12 personnel is that more often not it forces the defense to show you what they are going to do. For example the two TEs might convince them to bring a safety up and therefore make it obvious that they're thinking run.
Whether the players you have on the field are good enough to beat it though is another story.