You are using optional rules for your build so him using multiclassing is perfectly fair. And Darkness is not even as situational as many of your scenarios. You should do him the respect of reading what he wrote for you in response to your post, which is the same you wish others do with your posts.
Well, for sure multiclass is stronger than Single Classed. For obvious reasons.
And still depend on Darkness (Situational) to not be completely useless.
Remember before blaster, divine soul is a powerful spellcaster.
Even in the face of a Multiclass, I will continue Single Classed, proving the clear superiority.
ONE HIT K.O and True Necromancer (Divine Soul Subclass)
The Divine Soul Sorcerer Level 10 blasting.
Custom Lineage (+2 CHA and a feat)
Feats: Skill Expert (+1 Cha, Deception) Metamagic Adept (+2 SP and extra 2 metamagic choices), Inspiring Leadership.
Metamagic: Seeking Spell, Empower Spell, Quicken Spell, Extended, Subtle and 12 Sorcery Points
Prepare Subtle 5th Spirit Shroud when you are hidden and attack with 5th Scorching Ray.
With Empower Spell 1d6 has average damage 4,25, 1d8 (5.5), 1d10 (6,25)
Action: Twinned Firebolt for 23,5 avg damage per target
Bonus Action: Empowered Quickened Scorching Ray : 19,5 avg damage (2d6 +2d8) per each Ray
If the attack fails, so Seeking Spell rerolls, if Seeking Spell fails, Lucky feat rerolls. (LOL)
Favored by the gods add +2d4 attack roll. (once)
Total damage: Twinned Firebolt for 47 damage and Scorching Ray 117 damage = 164 damage.
About Seeking Spell, you use Seeking spell if
your attack fails
Empower Spell, you apply it if
your dice rolls is bad.
It deals fire and cold damage, It's insane thematically.
The True Necromancer
Why necromancy? It will act as an enhanced version of Mirror Image.
Divine Soul controls several Undeads that have HP buffed with Inspiring Leadership +14 HP and Extended Aid Spell that will act as a powerful Mirror Image.
Extended Seeming Spell serves to disguise the Divine Soul Sorcerer himself and his creatures in any creature. The Undeads wear black robes and masks that cover their entire bodies. 3 disguise chambers:
1: Expertise on Deception with Magical Guidance for rerolls
2: Disguise Kit as another layer of disguise that still applies Magical Guidance
3: Seeming Spell that will prevent the target from being able to distinguish the real target. The Undeads are physically and magically disguised as the Divine Soul Sorcerer.
4: The Divine Soul Sorcerer casts Subtle spell to prevent the enemy from realizing that there is a spellcaster in disguise there. Divine Soul does not use Verbal and Somatic Components.
This in practice forms a kage bunshin no jutsu of Naruto.
In addition to being an improved version of Mirror Image. Undeads can use Help action, Shove, Attack with Longbow at 600ft, use Search action
to find any hidden targets, etc. 20 Undeads can deal 130 damage
per turn for 24 hours. The Skeleton's HP is 26, with Aid Spell goes to 42.
These creatures are not easy to kill and are not separated to avoid AoE effects.
Inspiring Leadership, Aid Spell, Undead's help action, grappling make your party love you.
So, I'm going to build more of that level without a multiclass and that doesn't depend on specific conditions.
Thematically, Spirit Shroud, Animate Undead and Subtle Spell is really amazing. Seeming Spell is a fun spell for your creativity.
And most of all, it's really fun to party.