The Crimson Binome
Hero
So you're ignoring Prayer of Healing as a reference point, because you think it's poorly designed? Okay, sure. There are plenty of spells in this edition that are poorly designed and should be ignored, so let's pretend that this is one of them.All that means nothing if you consider prayer of healing as underpowered which was the very first premise of my last post.
That leaves our only reference point as Cure Wounds II, which heals 13 points over the course of one round.
Healing Spirit (as written) heals up to 210 points over the course of ten rounds. Even if it only lasts for one round, that's still 6d6 healing, so right off the bat it's already overpowered for out-of-combat healing when compared to Cure Wounds. But then it keeps going, maintaining that effect for ten rounds. It has better throughput with its one spell slot than if you had spent ten spell slots on Cure Wounds. It is very obviously ridiculously overpowered, in comparison to the only alternative.
Healing Spirit (limited to once per round) heals 35 points over the course of ten rounds. It has 2-3 times as much healing as Cure Wounds II, but you can divide it in 1d6 increments to be more efficient, and it takes ten times as long to achieve the effect. That's definitely a tradeoff, so it's not obvious that it's ridiculously overpowered. That version could be balanced, if you're ever in a situation where you aren't sure if you have a full minute before someone breaks down the door. Is that something that happens to people? Because if you can spare a minute safely, then it's right back to being ridiculously overpowered compared to the alternative.