Are you serious?

Clerics are powerful, if they don't lose their powers upon induction in Battle the game balance is dead.

Just imagine a funny group of ragers summoning, dispeling and bashing poor mages.
And if you leave them any window to gang to people, they will gang.

Another thing.
Ragers don't need additional powers do deal with mages. Spellbane is good enough to give mages headache.
Ragers don't die to mages as often as they die to communers, sanced warriors, bards and other classes ( sometimes boosted up by mages )