Nature mages do not get targeted as often as combat mages because they don't use curses, they don't do much damage compared to others. Although I agree that Vine is the most damaging spell, look at how long it takes her to cast it
. She could be killed before the vine comes out
. Nature mages simply can't beat, for example, a Lightning mage when it comes to DPS. Combat mage still stands towering in the damage department until, your fighter or ranger gets uber equipment and has both Critical skills maxed out.