Mark of the Storm blaster sorceror (2024), looking for a subclass

The build is almost entirely subclass independent, which puts me in the weird position of not being sure which subclass I want to do.  

Getting Mark of the Storm requires a specific background (House Lyrandar Heir) as it is not an origin feat, but Mark of the Storm does a couple of cool things for the build, the most important of which is access to Conjure Minor Elementals without requiring a multiclass.  But making good use of CME also means being in close, so getting Acrobatics proficiency (from the background) and +1d4 on rolls helps keep the character out of grapples.  And resistance to a damage type is never a bad thing.  (The rest of the spell list has some situational spells).

Current build thoughts:

19 levels of Sorceror, 1 level of Warlock taken either at 11th or 13th level (for eldritch blast, probably pick up Pact of the Chain?)

Starting Attributes: 8 Str, 15+1 Dex, 14 Con, 8 Int, 10 Wis, 15+2 Cha

Species: Astral Elf (bonus action 30' teleport that's not a spell, choose a skill and tool proficiency after a LR, useless cantrip, + normal elf stuff)

Feats: Elven Accuracy (+1 Cha), Potent Dragonmark (+1 Cha), Spell Sniper (+1 Cha), ... +2 Con OR Resilient Dex?, EB: something defensive OR Irresistible Offense (Dex)

Innate Sorcery + Elven Accuracy = 3 d20 rolls for every attack unless I have disadvantage.  Potent Dragonmark gets me all the spells on the mark list prepared in addition to normal spells known, +1 extra spell slot that can be used on dragonmark spells only, which will be a CME casting.  And that could mean rather frequent crits when Irresistible Offense rolls around.

Metamagic: 2nd: Extended, Transmuted? (for Scorching Ray), 10th: Quickened, Twinned (works on Scorching Ray, else Subtle), 17th: Subtle, Seeking?, Empowered? (Does it really matter at this point?)

Key spells and play dynamic:

The goal is to do massive single target damage with CME.  This means my concentration spell is spoken for most combats by late tier 2.  Critical attack spells will be Scorching Ray (upcast when feasible) and Eldritch Blast (tier 3).  (Sorcerous Burst will be the tier 1-2 cantrip of choice).  Extended spell gives me advantage on concentration saves for maintaining CME, and at the extended 20 minute duration it may last a second combat.  At later levels, quickened will be quite useful, so the build is also going to be sorcery point hungry.

Obviously this means most of my higher level spell slots are going to be consumed by upcasting CME and Scorching Ray, so the rest of my spell list wants to focus on defensive spells which don't require concentration, and spells which are useful out-of-combat.

Defense: Extended Mage Armor is obvious.  Shield for spot defense.  Mirror Image and Blink require no concentration.  Maybe Fire Shield? (No concentration, pick up a resistance).  

Utility: Seeming looks like an obvious pick with Extended Spell - 8h duration and no concentration.  See Invisibility to foil one of the most common forms of disadvantage (which, stupidly enough, also lets you see creatures which are hiding...).  And the usual things like Dim Door.  Time Stop is actually useful for those major fights, as all of Mirror Image, Blink, CME, and Fire Shield could be productively cast during it.   And there's probably plenty of room for Fireball for weak mobs.

Which brings us to subclass... i don't need one for anything.  I'm generally ignoring save-based spells as a combat strategy, so aberrant is out.  So let's see what the reasonable options look like:

Clockwork: Decent spell list (Aid, lesser/greater restoration, freedom of movement, dispel magic, wall of force), Restore Balance (okay utility), Bastion of Law (good defense, sorcery point hungry), Trance of Order (probably fairly low value given the investment of the build into advantage), Clockwork Cavalcade (good utility, expensive to use more than once/LR).  Good utility/defense, but really sorcery point hungry.  Decent extra spells known.

Divine Soul: +1 prepared spells (cleric list), access to cleric list (has some good things with Extended, like Aid and Deathward), Favored by the Gods (defensive primarily), improved healing (meh for this build), wings at-will (useful), and recover a ton of hp.  Good utility/defense, doesn't interfere with sorcery points, only 1 extra spell.

Draconic: +1hp/level, no need for mage armor, a couple useful spells (Arcane Eye is the most interesting pickup, Fly is good and Chromatic Orb is okay).  Gain a resistance. Wings for up to an hour (cost to re-use).  Meh summon. Honestly, the only reason to pick this would be to get Arcane Eye...

Shadow: Spell list kinda crap for this concept, DV 120' and blindsight 10', Cha save to stay standing when reduced to 0, Beast of Ill-Omen (doesn't synergize), bonus action conditional teleport, Umbral Form (is awesome).  Doesn't feel thematic, and the truly good pickup is very late.

Spellfire: Spellfire Burst (meh), decent spell list (scorching ray frees up a spell preparation, plus fire shield, lesser/greater restoration, dispel magic, aura of vitality), + counterspell that returns sorcery points, Honed Spellfire (still meh), Crown of Spellfire (good defense).  Despite two kinda sad abilities, its a solid spell list, plus a good ability that can generate spell points and a great final ability.

Wild Magic: No extra prepared spells, access to wild magic table, modify d20 rolls at the cost of sorcery points, and some improved wild magic table abilities.  Looks fun but unpredictable.

Draconic and Shadow don't look good.  Clockwork puts too much pressure on sorcery points.  That seems to leave Divine Soul, Spellfire, and Wild Magic as the reasonable choices, but I'm not sure how to value Wild Magic here...  Anyone have thoughts on the subclass?

(Build is allowed to use any official WotC product.  Must use updated 2024 version if one exists, but 2014 legacy material otherwise okay).