Sadida, Mask, Eca, and Osa can all heal. A Xelor seems mandatory as it's the only other class that can 'Raise' a party member. The team would have to be well coordinated because the lack of strong timely heals that a good Eni can provide may be missing.
Sadi has great heal potential but the setup and difficulty is much greater.
Masks do have some good numbers when it comes to healing. They would be the best option to get healing on turn one.
Eca's to me only feel like a supplement to the main healer. They would be nice to have as a fall back if the other healer in a group isn't quite up to the task.
I do not know much about Osa healing and am reluctant to use one.
The team may need to use tactics that suit my choice of healer. This will impact the other classes in the team.
What would be your six person team to attempt to complete all content? There are two rules, no Eni's, and the team must be made up of six different classes.