You keep talking about more variety as if I’m arguing for less, when the opposite is true. We disagree on where that variety should live, or how it’s accessed.
I don’t think you’re arguing
for less variety, I think you’re arguing
against different casting classes having different casting systems, and a desire for more variety is the reason I’m arguing
for that.
You often seem to be replying to something completely different from what I’ve said, as is happening in this discussion. As if I were making a point wholly disconnected from the point I’m making.
It’s hard to conclude that you understand what point I’m making when you reply to a statement about individualizing choice of Spellcasting type with a unified default as if I were talking about every character having exactly the same casting features.

I’m responding to the words you write, and when you try to clarify your meaning, you don’t seem to be giving me information I hadn’t already gleaned from those words.
I disagree. I…view this statement as completely false. The wizard is the most defined by thier Spellcasting, to thier detriment, and every other full caster has either another very significant feature and a smattering of others, or just a variety of features. The cleric has nearly as much going on outside of spells as a half-caster, as does the Bard. The warlock is almost more invocations and boons and patron features than spells, and the sorcerer’s spell list is overshadowed IME by sorcery points and meta-magic, and then also has origin features.
I find the majority of those features to have far less significant impact on gameplay than spellcasting does for
most full casters. The Warlock is of course the exception; it actually plays and feels meaningfully different from the other casters, and with various combinations of spell selection, patron, pact boon, and invocations, they can be made to play meaningfully differently even than other warlocks (though admittedly the sheer effectiveness of EB spam does make doing so less appealing from an optimization standpoint). It’s great and I want to see
more of that kind of diverse gameplay. In comparison, every other spellcaster feels cookie-cutter. Moon Druids do feel appreciably different too, because wild shape completely alters your character and their capabilities. But sorcery points and Metamagic overshadowing their spellcasting? Really? To me they feel like the seasoning, while spellcasting is the meal. They give sorcerers a dash of their own flavor, but fundamentally they still pretty much taste like wizards.
I struggle to see how you can see the very different spells of the wizard and Druid as “not significantly different”, as someone who does see the different classes powers in 4e as significantly different.
Their spells are different, but unlike 4e powers they don’t lead to significantly different gameplay. The options you weigh as a player, both round to round and level to level, are basically the same.
and I think that very harmony is disrupted by each and every spellcaster having their own underlying system rather than only the spellcasters who are narratively “weird” having different systems.
Well maybe this is part of the problem. I think every caster should be “narratively weird.” If they aren’t doing meaningfully different forms of magic, why are they different classes?