Is this homebrew "Elemental Air patron" warlock subclass balanced?

Question

I have created a new subclass for warlocks that is designed to be an option for those who would like to make a pact with a djinn or other mighty creature of Elemental Air.

Is this balanced as compared to the other warlock patrons?

Elemental Air patron

Bonus Cantrip

You know the gust cantrip, and it does not count against your warlock cantrips known.

Additional cantrips are not that unusual for subclasses, like the Celestial. I'm not really worried about this one.

Expanded Spell List

The following spells are added to the warlock spell list for you.

1st level: feather fall, thunderwave
3rd level: gust of wind, levitate
7th level: call lightning, wind wall
9th level: storm sphere, freedom of movement
5th level: cone of cold, control winds

I'm hoping these spells aren't too powerful for the warlock.

Storm Speaker

You have been endowed with the ability to communicate with creatures of elemental air. You speak, read, and write Auran.

One added language should not change power level that much.

Storm Wielder

Starting at 1st level, when you cast a warlock spell of 1st level or higher that deals acid, cold, fire, force, necrotic, poison, psychic or radiant damage, you can change the damage type to thunder or lightning (your choice).

Seems powerful, but I'm hoping that limiting it to lightning and thunder damage will keep it from being overpowered.

Storm Surge

Starting at 6th level, when you deal damage to a creature, you can deal extra thunder or lightning damage (your choice) equal to half your warlock level. Once you use this feature, you can’t use it again until you finish a short or long rest.

This one might be underpowered, but I can't tell.

Storm Shield

At 10th level, you gain resistance to thunder and lightning damage. In addition, you take no damage from falling.

This one seems fine, but I can't really tell.

Wind Walker

Starting at 14th level, you have a flying speed of 60 feet, and attacks against you involving arrows and other similar projectiles (i.e. not boulders thrown by a giant) are made at disadvantage while you are flying.

I'm pretty sure this is good but, again, can't tell.

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Is this warlock subclass balanced in comparison to the other official warlock subclasses?

Answer 1

Fairly balanced on average, but there are issues

This patron is fairly balanced overall, but some of the individual features are a bit under or overpowered for their level. The theme of the class is awesome and most of it is really well thought out.

Lets go through the features:

Bonus Cantrip

The Celestial patron grants two cantrips (light and sacred flame) both of which are more useful than gust. This feature is fine and fits the theme nicely.

Expanded Spell List

Your spell selections are all of the correct level and work with the theme of the patron. I don't see any of them being too strong as warlock spells. No issues here.

Storm Speaker

A free language and a very situational communication ability. This is strictly weaker than the Awakened Mind feature of The Great Old One patron, but that patron does not grant a bonus cantrip. This is balanced and not an issue. Though so situational it may not come up often unless your DM specifically plans for it.

Storm Wielder

This is a neat feature, but likely less powerful than you believe it is. Lightning and Thunder are both commonly resisted damage types (see this answer). Notable no creatures are vulnerable to lightning and only one is vulnerable to thunder. Therefore this feature will only be situationally useful, most of the time you will be equal or better off sticking with the base damage type for your spells.

There is one exception to this. A multi-class with Tempest Domain cleric and their Channel Divinity: Destructive Wrath ability would be extremely powerful. I don't believe it makes this feature overpowered, but is something to be wary of. If issues arise during playtesting, be prepared to remove this feature.

Storm Surge

You are right to think this ability is underpowered. At 6th level, it deals a total of 3 additional points of damage per short rest, scaling up to 10 at 20th level. This is severely underpowered compared to the features available to the other patrons.

I suggest looking at the Radiant Soul feature from the Celestial patron and adapting it to lightning or thunder damage instead of radiant or fire. Beware of interactions with your Storm Wielder feature if you do this however.

Storm Shield

If you take my advice regarding Storm Surge at 6th level you will already have half of this feature at a lower level. That said resistance to two damage types is quite well balanced with what the other patrons receive at this level. This feature is fine but may need to be modified based on the changes to Storm Surge.

Wind Walker

A fly speed is amazing; it is one of the best features you can grant. The Storm Sorcery sorcerous origin grants a similar feature, Wind Soul, at 18th level. That feature comes with some additional abilities that make it worthy of the higher level though. The Divine Soul origin grants also grants a 30-foot fly speed at 14th level.

You might have noticed I am comparing this feature to the sorcerer subclasses rather than warlock. That is because this feature is very different to anything granted by the other patrons. The others mostly grant a single-target ability, often only once per rest too.

Disadvantage on attacks from light projectiles is just an added bonus on top of an already strong feature. I would consider moving this part down to 10th level and just leaving this feature as flight alone. That would make it more balanced.

Currently this feature is overpowered compared to the other patrons, but it is clearly the core feature of the patron and I don't want to tell you to take it away. You could also consider limiting the duration and granting a limited number of uses per short rest or similar.

Summary

Overall, the balance of this patron isn't too bad. You could probably playtest as is without major issues. You start off strong but then have fairly poor progression up until 14th level where you gain your best feature. With some minor tweaks, I would allow this for playtesting at my table, but be wary of the Tempest Domain cleric multiclass.