I am quite aware 
This was, naturally, more about potential - or wishful thinking, if you want - than reality. However, I do get the impression that time is running out for the Imperium, that some things must change or they'll lose the war against the qunari. The magisters care more about their internal rivalries than about winning the war and doing something for their empire, and in addition, Tevinter needs allies, and for that it needs to be someone wanted as an ally. People like Calpernia and Dorian are needed, and Calpernia comes across to me as the better leader. She has the commanding presence and the determination Dorian lacks, for all his extraordinary abilities and good intentions.
Dorian doesn't seem like he really wants to become Archon. He wants to make the Imperium a better place, but he doesn't have a concrete plan. He has a bit of Carver to him, he has the potential for greatness but he hasn't found the right opportunity yet.
Calpernia has the ambition to lead Tevinter and she could do it, but being an ex-slave with an army of former cultists won't go to far with the Senate. Dorian has the experience with the upper classes and the support of other progressive Magisters like Maevrais. They could work together.