I prefered the flavor of herbalist. Healing when you join the team doesn't seem to be the way cleric works, is it? I like the idea that the bonus grows the bigger the team is though, so maybe it's more a matter of flavor. I would imagine something like a priest/paladdin that gets more fervour :)
I was thinking of making it prevent damage to each member of the team, but that seems a bit strong.
Yeah, it doesn't feel very cleric-y. Still, I kinda like it.