You actually think Hawke could have defeated the army of Templars that was left?
What makes you think those numbers were equal? Most, if not all, prisons in the world have more inmates than guards.
And need I remind that the White Spire was the only Circle who actually suceeded in killing the Templars stationed there?
Yeah Hawke would have easily killed them, Hawke defeated an ancient magister, a harvester, a behemoth to be (Meredith). Some puny maniacs who think maker is on their side would be a breeze. How else do you explain their fear? They were afraid of Hawke, plain and simple and regardless of the side you chose.
Don't forget that Kirkwall was famous for the number of its Templars so I doubt there was less than equal number to mages. Besides you have to consider the unusual number of tranquils in Kirkwall too.
There isn't enough info on to make that assumption, all we know is the fact that 14/15 circles break free, how we don't know. I wager in some of them most Templars were killed and in some of them mages barely escaped by killing enough and opening the way and sustaining casualties.