Opinion.
It has been answered before. Group content of any difficulty level should have enough damage that bringing a healer is required no matter your skill level--the sustain provided by non-healer jobs is not powerful and/or frequent enough to replace the accessible healing provided by healer jobs. This can be accomplished by either increasing the frequency of unavoidable damage, pruning or limited non-healer sustain, or a combination of both. Moreover, Ultimate should have high enough outgoing damage that healing through tests your ability to managing all of your healing resources.
1. Balance outgoing damage around what healing healers can provide. Easier content can still be forgiving, but if you're going to give jobs like White Mage and Sage free healing resources every 20 seconds, for example, give those healers reasons to use those.
2. Create opportunities for the healer to make decisions within their own toolkit. As a small example, rather than putting a cooldown on something, give it a steep MP cost with no cooldown. Make the player choose when to take advantage of whatever potent effect that spell has by managing their MP rather than just waiting for it to be ready again.
3. Reward optimal healing with fun and interesting gameplay. For most people, that means more interesting DPS rotations that allow you to shorten the duration of an encounter and increase the rest of your party's margin for error. I'm sorry that you're in a select minority of gamers who find damage extremely unappealing, but that's generally what most gamers look for in video games; that includes players who opt for healing and support roles. There is a subset of players who prefer to focus on support. If only there was a job that rewarded optimal healing by empowering their teammates instead of themselves. That would ideally be what is designed to appeal to players within your subset.