Soloing dragons with a mage? You sure about that? The first time I played and completed the game back in 2014 I only played as a warrior so never tried any of the other builds out. Now I decided to try another build and was told mages normally get their asses kicked quickly.
If you got the right gear and materials you can spec mages to the point where you don't need anybody on your squad.
Way easier to do with Archers though.