I believe in out of the box thinking but then can imagine a box around that new idea, and no matter allowing white mage to both be main DD and main healer is a bad idea for balance.
This is an opinion and not a fact. It isn't and doesn't have to be "bad for balance" for CNJ/WHM to have damaging spells. This doesn't mean that nuking is its primary role. You're not the out-of-the-box thinker you claim to be if you're so opposed to this.

Heals and damage are in fact rarely completely isolated from each other. Very few games these days give the "healer" nothing to attack with- it simply isn't commonly used in endgame content except in special situations. These spells are however necessary for solo and PvP balance- quite contrary to your statement of it being bad for balance.

WHM/CNJ having a handful of situationally beneficial damage spells does not mean that th ey aren't going to be healers more often than not, nor does it mean dethroning some other job as the best source of damage.

My 2 cents. As long as whm AND cnj have some way to get decent amount of exp by themselves and without a party.
At least someone understands the primary reason those spells and abilities exist.