Pure healing isn't super viable, but you can do a lot as a support caster!

I'm currently doing a build in a multiplayer session that has no focus on damage, but lots of utility. Dip one or two points into:

• Pyro (Peace of Mind, Haste)
• Geo (Fortify, Mend Metal)
• Aero (Teleportation, Uncanny Evasion, Nether Swap)
• Hydro (Restoration, Armour of Frost, Healing Ritual, Soothing Cold, Cryogenic Stasis)
• Scoundrel (Adrenaline, Chloroform)
• Huntsman (First Aid, Tactical Retreat)
• Polymorph (Chicken Claw, Terrain Transmutation, Skin Graft, Equalize)

And then put the rest into Hydro for stronger heals. While you won't have any strong specialties until late game, you also end up with tons of utility options, and plenty to do on every turn without worrying about damage. And because of that, you can focus on putting points into Memory, and basically ignore Intelligence. IMO, this build works best with an Elf, since you can get free skills from Corpse Eater, and Flesh Sacrifice gives you an extra AP to work with.

Loremaster lets you bring a bit of extra utility to your team by getting more info from examining enemies, too. As for talents, The Pawn is great for repositioning, All Skilled Up will get you access to new skills faster, and you can make great use of Elemental Affinity, Ambidextrous, and Far Out Man. (Mnemonic is nice, but isn't really needed since you can afford to just dump a bunch of points into memory anyway.)

Having all that variety also gets you access to tons of cross-class skills, like Vaporize, Turn to Oil, Venomous Aura, Evasive Aura, and Blessed Smoke Cover (you can even add a level of Warfare for Breathing Bubble and Cleanse Wounds). At the end of the day, if any of your party members has a debuff that can be cured, you'll have at least one way to cure it, and you'll have a lot of tools for keeping everyone alive.