Yeah, unfortunately, you need rune mages or paladins to make it work.
Worse off is that the goblins and catapults all suffer from range penalties.
Rakush is unique in that he can single handedly handle the Ogre Set by himself.
Few heros can handle boots (besides Jimmy) and a belt too.
Combined with the +20% damage with catapults items and rakush, catapults do end up being stronger than most of the other ranged units, but not counting range penalties and the simple fact that they start off with such a negative resistance to fire.
This "might" work with a warrior or paladin build, but I find that pure range builds do not work well with mages (I've failed to make it work a couple of times now). Despite the flexibility, there just isn't enough raw damage due to low leadership to make it happen.
And the double cast advantage is nullified by the fact you have to cast so many spells to close that leadership damage gap.