For starters, suggesting that we use blood magic, a tool of demons, to combat demons is pretty funny. Second, Templars don't sit in Towers all they day. Hunting apostates. Defending Chantry land. Putting down rebellions in Kirkwall ever before Hawke went there. Finally, in the Last Straw, no matter the side, the Templars dominate the mages. If Cullen had not let the Champion leave, they would very likely be dead if siding with the mages. In Asunder, battle after battle ends with the mages being destroyed, even with blood magic at their disposal. The Templars have proven their skill. All the mages have proven is that they make nice pincushions for Templar blades.
That's a bit of stretch, Cullen steps backward in fear when the champion gives him "the look", the other Templars wet their pants. The female Templar waits until Hawke walks away quite a distance before daring to approach Meredith (which was where Hawke was standing) and see what happened. Go watch the ending again.
Without Hawke Cullen would have died in the wounded cost and more Templars would have gotten demons in them.
Also Orsino and his mages managed to kill all Templars stationed in the circle before Meredith arrived with rest of the order. This usually happens, in same number templars get decimated. Mages rebel, mages usually win, Templars retreat and come with more numbers, mages either lose or flee. The Templars ALWAYS count on numbers, best equipment and favor of people to win against mages. Now that all of it or at least most of it is gone the mage vs templar war in Inquisition is quite balanced. Not to mention the mages possess one of the most fortified holds in Thedas.
Also the Templars of white spire get slaughtered and mages escape before Lambert arrives. Again in equal numbers to mages Templars always go boom.