The developers said Cullen is supposed to be a "moderate" templar, so I don't see why his words should be dismissed. In that scene, he's explaining why the Grand Cleric needs to support the templars.
Religion plays a constant role, in the formation of the Chantry controlled Circles, the view of magic among Andrastians, and even in the recruitment of templars. In the Gallows (when the Champion supports the mages and opposes the Right of Annulment), Bethany even talks about how her religious beliefs are the reason she originally thought mages belonged in the Circle.
Note offhandly i don't care either way to be honest.
Divine Right is subject to interpretation by given the Templars are a Chantry institution it does make a sense, but again its one random sentence in the entire game.
How much evidence is that? And given moderate or no it was a rewrote character who said as much.
And Religion is a good enough reason as any to do what must be done to contain magic.
If practicality doesn't work, Faith might.