Healing spells for anything that's not a Life domain cleric are horribly undertuned. Life domain cleric is pretty much mandatory to make healing spells not trash and worthwhile over throwing health potions.
For reference, a Mass Cure Wounds, for a whopping lv5 spell slot, cures for a measly 17-25 health. Channel Divinity from Life cleric, 2 charges per short rest, heals aoe for 40. Healing spells are absolutely worthless outside life domain cleric passives propping them up, just throw potions at people instead for far superior healing. It's not like potions are hard to come by.
If Larian wanted Bard or Druid to be alternatives to cleric, they failed miserably. Between Channel Divinity, Bless, Sanctuary, and Life Domain sub perks, cleric cannot be supplanted as a class in a party by either of those. They could easily make druid and bard possible alternatives to cleric if they gave them the life domain cleric passive to boost healing done and minimum heals, and gave Bless to both Druid and Bard spellbooks. The other problem is Bard and Druid, but especially druid, are strangled by 95% of the spellbook being concentration spells. Clerics only have to worry about Bless or Guardian spirits, and have plenty of powerful nonconcentration utility, heal, and nuke spells.
This has also bad gameplay impacts. You will feel compelled to run Shadowheart in your party every single playthrough instead of having alternative companion party comps unles you're willing to break RP and respec your companions.
I mean I think that it is exactly because of this that you SHOULDN'T feel compelled to run shadowheart.
5e has a different approach to healing from previous editions and a lot of other rpgs. They wanted to avoid battles of attrition with the healers propping people up. So in-combat heals are small, but potentially clutch. A single heal CAN make the difference in many cases. But very often those cases don't arise, and you don't want a healer, you want someone else with offensive options, which is why all healing classes also have a buffet of offensive options to choose from as well. Healing would be more useful for sustaining you over the course of a day if this game didn't have effectively infinite free rests, too.
But the point remains you can make do without a healer or with healing/damage mitigation capabilities spread out over multiple people instead of focused in just one class. It is absolutely not necessary to take shadowheart or a healing-focused character at all.
It is absolutely gamechanging.
I'm sorry, but a 40 HP aoe heal 4 charges total per long rest that applies 50% physical DR, bless with mystra staff from arcane tower for 2d4 attack rolls and saving throws, 3d4 spell attack roles is entirely game changing. So is sanctuary. In any good aligned playthrough where you want to keep ally NPC's alive or even in tougher fights like taking on Balthazar in the Shar Temple instead of at the Nightsong, or Orthon Yugir without dialogue checks, Shadowheart makes a world of a difference. It's not even close. She's adding over 20%+ increased hit rate, heals you for 1/3 of your health aoe, applies 50% physical DR, and makes you highly resistant in saving throws all in one button push while still having access to guardian spirits/insect plague/flamestrike and sitting on heavy armor with a shield at high AC with divine strike for when she needs to melee.
Bards and druids don't hold a candle to her as a force multiplier or a healer.
Could I replace her with 2 fighters (or 1 fighter, 1 paladin) 2 sorcs or 1 fighter, 1 bard, 2 sorcs? Sure, can make that work and kill things before it's a problem. There's a slight problem with that, none of your companions allow for that unless you're fine with discarding RP and retconning their origins and aesthetics.
If you're not retconning your companions and wish to respect class and character aesthetics, Shadowheart is absolutely miles ahead with Lazael and Karlach compared to the other companions, followed by Gale. Wyll, Halsin, Jaheira, and Minsc might as well be in the trash bin, and Astarion is not bad as rogue is pretty strong as well so you can sub a martial for him if yo like his story.
