And it certainly doesn’t make magic any less distinct, by any possible metric, to let the lesser magic users (still not clear on my sorcerers and warlocks are lesser magic users) have distinct spells that only they have.
It makes the 'greater' magic users seem like they're missing something. It might well be that there are spells only attractive to 'lesser,' say beause they leverage martial weapon use (all those ranger archer spells), that the greater caster can technically cast, but never bothers to.
DISCUSSION POINTS:
Aganazzar's Scorcher (Druid*/Wizard) (S,W)
For the fire element, I am leaning towards Druid. Wizard already has Burning Hands and Fireball. What decent Fire spells does the Druid have really?
Classic Druid fire spells included: Produce Flame, Flameblade, Produce Fire, Protection f/Fire, Heat Metal, Wall of Fire, Fire Seeds, Conjure Fire Elemental, Firestorm and Chariot of Sustarre.
Faerie Fire being a light rather than fire spell.
Maybe I place more value on theme and tradition, but I'd just summarily give any named spell to the Wizard.
Alter Self (Druid*/Wizard) (S,W)
For the shape-shifting idea, as well as developing natural weapons, I thought Druid would be better for this spell. If it was an Illusion, such as Disguise Self, I would totally think more Wizard (which is why Disguise Self stayed with Wizard).
Disguise Self to the Wizard (illusionist) and Alter Self to the Druid sounds equitable.
The Druid eventually got A Thousand Faces, as really it's only claim to the spell anyway, so you could use that as an ability instead of a spell?
Blindness/Deafness (Cleric/ Druid*) (B,C,S,W)
I went with Cleric, TwoSix with Druid, which I get because this is a necro spell. I'd be fine with committing this to Druid given the somewhat curse-like nature of the spell--very witchy.
Classic 'Reversed' Cure/Remove spell for the old EHP, I'd say Cleric.
Continual Flame (Druid*/Wizard) (C,W)
I was thinking Druid but just remembered this isn't actual flame (no heat, no oxygen use). I guess we could think of it as an upgrade from Dancing Lights and commit it to Wizard?
Yep, Wizard. Continual Light was originally both a Cleric & a Wizard spell, but the Wiz got it a level lower. And, the continual flame version is less divine glory, more magic tricks.
Crown of Madness (Wizard/Cleric*) (B,S,War,W)
I think I understand why TwoSix went Cleric, given the Cleric/Warlock comparison, and it also affects humanoids, a core concept for Cleric in this exercise. However, given the brutal, controlling nature of this spell I thought Wizard would be a better fit.
It's originally a fey warlock spell, so you could toss it to the Druid on the fey-association theory.
Flaming Sphere (Wizard/Druid) (D,W)
Coin toss?

This could go either way for just about any reason. I think wherever we place Aganazzar's Scorcher, Flaming Sphere should go to the other list.
Originally Wizard. Not really very druidy in feel, IMHO. A druid would more reasonably conjure an elemental.
Gentle Repose (Cleric/ Druid*) (C,W)
Although necrotic, this spell is protection-oriented IMO and should fall under the Cleric's list.
Now you're getting into support spells where it's hard to say they should be exclusive. There'll be more as we continue.
Locate Object (Cleric/Wizard) (B,C,D,P,R,W)
Sigh... the "Locate" spells... I just don't know and I can see good arguments for any list really.
Any divination runs up against the issue that, IRL, all traditions of magic were big on divination.
Finding a lost something, though, feels more like a parlor trick than a miracle. Save Find the Path for the Cleric, let the wizard have Locate ____.
Ray of Enfeeblement (Cleric*/Druid*) (War,W)
Another classic wizard spell. Also, 4e "laser clerics" aside, rays should be the wizard's thing - it flirts with sci-fi more than the cleric.
Scorching Ray (Druid*/Wizard) (S,W)
Ah, another fire-based attack spell. There are a lot of those in 2nd level spells! No great thought about this one, Fire = Druid, but Wizard spell currently and at this point both classes have sufficient fire-attack spells. I think this will come down to a balance between the different fire spells and just who is better served and represented by which one.
IIRC, this was long ago broken out from magic-user the Flame Arrow spell. And it's a ray.
Shatter (Cleric*/Wizard) (B,S,War,W)
This is pretty much a straight AoE arcane spell, so I'll probably end up differing it, but man, I love the Cleric-Thunder concept a lot... sigh...
There's always Domain spell exceptions.
Silence (Cleric/Wizard*) (B,C,R)
For me this is a classic Cleric spell,
Agreed.