Tbh, "support" is not applicable to mages at that lvl. Now, you see tank mages go 22-23 and use BOM BOV, in which their plat packs substitute for armor when they have low BOV. They also bring 3+ heal so they don't really die unless you "nuke" them. 15-17 dex mage is also pretty fun. You could also try 22-23 dex mage.