So, as a follow-up to this question about giving extra spells to sorcerers, inspired by the second half of András' answer to that question, some of the spells I have chosen are from other spell lists.

Note that this question assumes that it's a great idea to give sorcerers extra spells (regardless of whether that's true or not), and anything to do with that aspect of my idea should be an answer to my other question; this question is about whether these 10 specific not-normally-sorcerer spells (see below) would create balance issues in the hands of a Sorcerer with access to all their Metamagic.

So, these are the 10 spells I've picked for the various sorcerer archetypes that don't already come from the sorcerer spell list (I'm focusing on only these 10 spells to narrow down the scope; hopefully assessing only 10 spells isn't still too broad for one question, but one question per spell sounds insane, and I didn't know how else to meaningfully divide it up):

• 
  Elemental Bane (for Draconic Bloodline sorcerers)


• 
  Aura of Vitality (for Divine Soul sorcerers)


• 
  Aura of Life (for Divine Soul sorcerers)


• 
  Circle of Power (for Divine Soul sorcerers)


• 
  Inflict Wounds (for Shadow Magic sorcerers)


• 
  Vampiric Touch (for Shadow Magic sorcerers)


• 
  Shadow of Moil (for Shadow Magic sorcerers)


• 
  Negative Energy Flood (for Shadow Magic sorcerers)


• 
  Call Lightning (for Storm Sorcery sorcerers)


• 
  Destructive Wave (for Storm Sorcery sorcerers)

The only reason that I can think of why these would be a problem for a Sorcerer to have is because of how they might interact with Metamagic. In other words, trying to game the system in new ways thanks to the availability of these spells.

So are there any serious balance issues that would arise from Sorcerers using Metamagic with any of these spells? Or any other reasons besides Metamagic that would cause a problem (if my assumption that Metamagic is the only issue is wrong)?

It is mostly fine

Aura of Vitality with the Extended spell metamagic is very potent, you could out-heal a Life Cleric.

I would change that one.

Aura spells

Sorcerers are not really capable to be in the front line without multiclassing, so they do not benefit much of combat related spells that need close proximity, like Shadow of Moil, Aura of Life or Circle of Power.

Repeated Damage

Call Lightning and Vampiric Touch are greatly improved by Quickened Spell.

Vampiric Touch needs close proximity, probably costing you more in HP than you gain, so it is not a problem. I think it is actually too weak without Quickened Spell.

Call Lightning is quite limited by the 100 feet ceiling requirement, so it is also fine.

Negative Energy Flood

Without Animate Dead, this does not have much abuse potential.

Destructive Wave

This spell does as much damage as a Fireball in a 5th level slot, but the damage type is inarguably better, and very party friendly. However, it is best used from the middle of the enemy group, not really suitable for Sorcerers.

Elemental Bane

One of the weakest spells in the game. Targets only one creature, requires concentration, allows a save, does not help with immunity, and the 2d6 extra damage is only applicable once per turn. All of this for a 4th level slot.

Draconic Sorcerers are much better off with the Elemental Adept feat, no amount of metamagic will make this spell good.

Multiclassing

I do not agree with NathanS' answer that everything that could be reached by multiclassing cannot be overpowered.

Multiclassing has its own cost, delayed features, MAD (Multiple Ability Dependency), delayed or reduced ASIs. With these additional spells you get the benefits, but none of the downsides.

So these spells could be overpowered (but are not).

There is no impact on balance that didn't already exist via multiclassing

Just before posting this question, I noticed this suggested related question: Does a sorcerer's metamagic work for non-sorcerer spells?

The answers explain how Metamagic could be applied to any spells you know, not just those you learned as a Sorcerer. Therefore, any of the Cleric, Druid or Wizard spells from my list that are not normally for Sorcerers could be Metamagic'd by multiclassing into those classes. Even the highest level Paladin spells I suggested could be Metamagic'd if you had a Paladin 17/Sorcerer 3 character, or a Bard 10+/Sorcerer 3+ character (due to Magical Secrets).

Of course, there are a few caveats; with the Paladin spells, the minimum level this could be done (with the 5th level spells specifically like circle of power or destructive wave) would be level 13 (Bard 10/Sorcerer 3), whereas these Sorcerers with my free spells would be able to do the same at level 9. Not a huge difference, but they are different tier PCs, so it's something worth pointing out.

Also, some of my lists mix spell lists, such as my Shadow Sorcery lists including inflict wounds (Cleric) and vampiric touch/shadow of moil/negative energy flood (Wizard; Warlock too, I think). A 1 level dip in Cleric could allow such Metamagic'd spells with little cost, though, if someone were happy with a Wizard 9+/Sorcerer 3+/Cleric 1+. But then there's my Storm Sorcerers with access to both call lightning (Druid) and destructive wave (Paladin). This could only be achieved by going Bard 10/Druid 5/Sorcerer 3 (with two more levels to play with) so a level 18 PC minimum, whereas my Storm Sorcerers could do this at level 9.

Furthermore, given that these particular multiclassed builds (the ones in my previous paragraph) mix classes that use different spellcasting stats, these characters would also be behind in terms of spell attack bonus and spell save DC values for those spells, unless they happened to have matching stats in INT, WIS and CHA (where relevant). So my Sorcerers would have that advantage over those multiclassed PCs as well.

However, I can't think of any way that these particular spells can be made to interact with each other, even when using Metamagic, in a way that would cause any major balance issues, and therefore I don't think the availability of such options being available at earlier levels (i.e. the option to Metamagic call lightning and destructive wave at level 9) would cause any problems.

Hence my conclusion is that multiclassing already provides any potential ways to unbalance things, so giving a couple of spells from different lists to Sorcerers for free won't hugely affect anything other than gaining the ability to do so a few levels earlier.

Anytime you give a spellcaster access to more spells, it increases their power level. Consider that the primary power of a Divine Soul is the access to extra spells.

That said, a few spells isn't going to be a big difference. Certainly not enough to cause any trouble at your table. There are no spells there that are overly ripe for metamagic abuse, certainly none that compare with spells already on the Sorcerer spell list (like Polymorph for example).

More directly than any of the other answers: no, there is absolutely no balance concerns, because the assignment of spells to particular spell lists is entirely flavor-based.

See Mike Mearls' tweet that spell list-swapping is power-neutral:

swapping spell lists is essentially power neutral #WOTCstaff

In other words, all spells of a given spell level are intended to be roughly equivalent in power, and spell lists are put together solely to help differentiate the casting classes flavor-wise - healing is kept to the divine classes, sorcerors get "simpler" spells, warlocks get lots of scaling spells and avoid concentration ones, etc. No list is more or less powerful than any other in general.