It was never grossly unbalanced you can't just look at the spell in a vacuum but class access to spells as well. Classes like cleric did not have access to healing spirit. The spell helped classes with more limited healing abilities heal like the druid and the ranger. As it stands the nerf buffs clerics and paladins which did not need buffing and nerfs classes like the ranger which definitely does NOT need any nerfs. When considering the power of spell you can't look at it in a vacuum because spells don't exist in a vacuum.
You're right, I don't look at a spell in a vacuum. I look at spells in comparison to other spells because spells are ranked by spell level and class has nothing to do with it. I would point out that an argument in a vacuum white room trumps the lack of any evidence to the contrary that occurs in gameplay that you provided. Claiming it's a vacuum does not prove any point you might be trying to convince me of.
This is a fact: Out of combat in it's current version allows healing spirit to give 10d6 hp in healing to every member of the party. In a party of 3 that's 105 hp. In a party of 4 that's 140 hp. In a party of 5 that's 175 hp. That's in a 2nd level spell slot. Aura of healing, in a higher level slot, gives 70 hp to the party out of combat per casting. A 2nd level spell should never be better than a 3rd level spell when they both have the same function. That's unbalanced. Please prove otherwise.
Further, healing spirit costs a bonus action to cast and no further actions to maintain. Aura of healing costs an action to cast, and therefore an attack, and a bonus action to maintain. On top of that, aura of healing is restricted to one PC per round instead of on each turn in combat when it matters, and healing spring using the same slot heals the same 2d6 on top of all the other benefits it has over the higher level spell.
Healing word and cure wounds are not efficient healing at all.
Prayer of healing used to be the good out of combat healing spell. By your reasoning adding healing spirit was a buff to druids and rangers, and therefore a nerf to clerics and paladins. Fixing healing spirit cannot be a nerf when it's correcting a nerf.

Prayer of healing is the same spell level as healing spirit. Healing spirit takes a bonus action to cast, no action to maintain, can be used in combat, and heals more hit point damage out of combat. Out of combat healing spirit has healed more hit points than prayer of healing can 9 minutes before prayer of healing goes off. There's nothing but disadvantage for prayer of healing in comparison.
Mass cure wounds, a 5th level spell, requires an action to cast and heals 6 creatures 18.5 hp on average. That's 111 hp total, which is more than prayer of healing or aura of vitality (which makes sense), but less than the same number of creatures using a second level slot for healing spirit does. In combat, healing spirit in the same slot is 14 per target in the first round and doubled to 28 per target in the second round. For a bonus action spell. Second level spells should also not be out performing 5th level spells in the same slot.
That's not a vacuum. That's how the spells work in play and based on how spells are ranked. In combat there is at least a movement requirement but out of combat the spell was clearly ridiculous. A cap on the number of uses has nothing to do with nerfing or buffing any class. It's fixing something in the spell that needed fixing.