Wizards and subclasses - a bit of a deconstruction.
So, there are six full casting classes. Three support (cleric, bard, druid) and three ... blasters? mages? (warlock, wizard, sorcerer). Lets go with mages. This contrasts with the martials split into three tanky classes and three skirmisher classes.
As I said above, cleric, druid and bard are all primarily support classes. Healing and buffing is what these three are known for. But beyond that, each of the three classes has a different focus beyond healing and buffing. Clerics are kind of the iconic White Necromancer archetype - their iconic Channel Divinity has the power to Turn Undead (or, in previous editions, the power to control); they also have the most spells that directly deal with speaking to ghosts or those passed on, and Radiance magic is a common weakness of undead. Druids have quite a bit of an elemental theme going on, especially if you include wood as a fifth element. The lands, the environment, nature, call it what you will. Bards, obviously, are directly connected to mental-themed abilities, such as illusions, enchantments and touching on the psionic a bit.
Meanwhile, lets take a look at the three mages. Unlike the healer classes being split into three clear themes with their magic... well, wizard can pretty much cast whatever a warlock or sorcerer can, with only a small list of exceptions. The default, "simple" subclass for each of the three mages are an elemental blaster - fiend, evoker, dragon. They all have illusionist variants too (fey, illusion, abberant) as well as necromantic (hexblade/undead/undying, necromancer, divine/shadow). All things that we had split between three classes with the healers. With the mages, its all just kind of mixed together for each of the three.
IMHO, the only real difference between wizard, warlock and sorcerer is in the class features, not as much the spell lists. Even in the case of warlock and sorcerer, with smaller lists, most of the difference is made up by the subclass additions. When 90% of the class is defined by their spells... that's a bit of an issue, imho.
Now, we could argue that we should break the wizard, warlock and sorcerer down into separate spell lists, but I don't think that's realistically going to happen. Just like I don't expect to see a significant differences in spell lists. We're going to end up keeping at least one necromancer-themed subclass for each mage class.
I'd also say that this model is also going to continually hamper any inovation with the wizard.