2. Atlanta's offense needs three touchdowns
Yes, Arthur Smith is hurting this team when they get close to scoring with his calls. Despite this, you're the veteran quarterback and have a myriad of young weapons to get the job done against a terrible Arizona defense. If the Falcons cannot find a way to score the ball three times against this team, barring injury, go back to Desmond Ridder.
At least with Desmond, you can attempt to sell that you're developing a young quarterback. If the Falcons cannot score consistently against this defense there is no reason to stick with the veteran. Putting Heinicke in as the starter was an attempt to fix this offense and make a run at the playoffs.
There is also the fact that if Atlanta does manage to score three touchdowns that is the best three straight games of offense this team has been given all season. If it matches with the change to Taylor you have no choice but to name him the starter moving forward. This is only the case, however, if the Falcons both score consistently and find a way to win.