Mages only have 2 choices, Death fire touch or thunder lords, and 90 pecent of mages use thunderlords because DFG is so niche and is rarely better than thunderlords. Even damage over time mages can still thunderlords just as well.
Ad champs on the other hand can use Warlord bloodlust, fervor of battle, thunderlords, and the speed up keystone (cant remember the name). the can even use DFT if they want.
The point is, mages need another keystone option. I suggest removing DFT and replacing it with some more creative and healthy.