An issue with spellbats is that multiple bats don't really increase the damage output, and each individual bat does 1/3rd of the damage the focus would have originally done, at a much higher complexity cost of 8, compared to Projectile's 4. The mobs have a brief period of invunerability after a spellbat hit as well. Now a swarm of bats still do have a benefit (absorbing projectiles that would have been shot at you, doesn't matter if a few die, and a few other minor benefits).
They are definitely more fire and forget though. Just cast and keep moving, no aiming required.
They probably would work well with the healing focus though, although their complexity + heal focus complexity means you can't get that strong of a healing focus, and it is more of the regeneration effect than the bulk heal.