Actually I always thought that if Felix were to be in a KH setting he would be a pure healer instead, able to heal people by touching them with his magic hammer. (Plus he really doesn't seem combat trained anyway)
I also wanted Oner to be different than Reno in terms of fighting style and thus not have Oner be another Reno in terms of combat. Reno is the destruction artillery. Oner is the magic swordsman-monk/cleric who uses his own very large mana pool to enhance his fighting abilities and strengthen his attacks and I think giving him that ability that sets the two of them apart.