Arians loves the deep ball. That's never been Tom's game even when he was younger.
And here's something no one is talking about. The reason Brady is no longer a Patriot is because he has been collapsing against pressure for the last several seasons - at least two. Father time is catching up to him. If he was still performing as the Brady of old the Pats would have kept him.
So what we have is a QB who has always preferred surgically dissecting a defense with short to intermediate stuff, who was never mobile but getting less so given he's 43, and who's been severely declining under pressure. You put that QB in a new offensive scheme that calls for deep shots every other play and are surprised at the result? Against a Rams type defense that can get pressure and cover, last night is what we should expect Brady to look like.