Well some say so, some say otherwise. Its propabily save to say its intended but not necessary for a healer to use his/her damage spells.

So why not make it so damage spells actually give buffs to healing spells?

Here is an example on WHM: If you have Aero-3 up on an enemy you gain a 2% healing buff if you have aero 3 and aero up you get an 5 % healing buff. Also stone, hitng and enemy with a stone spell reduced the MP cost of you next healing spell by 1% and this can stack up to 10 times and 10%.

Would that not be a good way to incentive players to use all their tools and helping to fix the issue?