They are very weak early levels, level 5 and beyond they start scaling super hard.
Not at all, they spell have hit chance even if they are aoe. And most of those spells cannot one shot enemy. Most powerfull for early game is magic missle, or some elements combo but for this you need two or more mages.
In DOS I prefer to have 2-3 archers to shot water arrow + lighting arrow combo or oil + fire. Mage was usefull in really late and onyl for killing big guys.
