That's the thing about Wizards... I think there are actually like three different "types" of categorization that could have subclasses designed for them.
There's the "job" types... your Scribe, your Bladesinger, your Warmage. Has nothing to do with the types of spells they cast, but what they do with the magic they have available.
There's the "thematic" types... your Chronomage, your Pyrokineticist, your Force Mage The Wizards that specialize in one energy or type of spell to accomplish all different types of actions but which use a singular theme for how the magic looks.
Then there's the "style" types... which are your Spells Schools. These Wizards all focus on a singular style of magic where all the spells do a similar thing as part of the school, just at differing power levels and targets.
The game has made subclasses for all these three different types of categories. The question then becomes whether or not-- since the "style" type has a finite number of Schools that doesn't change-- it is important to fill out that one type before focusing or presenting ideas for the others. Some of us players who have Lawful/Ordered brains kind of appreciate/need for all eight schools to be filled out, because it just feels wrong otherwise. That's why I know I actually appreciated seeing all 8 subclasses in the 5E14 book because it just felt right. And while the 5E24 book will only have four of them... to me that isn't so bad because we still have the 5E14 ones available to bring forward as needed.
The one funny part though, is that in truth I think one of the eight classic Spell Schools really isn't like the others and actually shouldn't be one. One of the eight to my mind actually falls under the "thematic" type-- the Necromancer. The spells for the other seven all do the same sort of thing per group-- Divination spells gather information. Abjuration blocks and protects. Evocation blasts energy. Conjuration brings things into existence. Enchantment controls the mind. Illusion deceives the mind. Transmutation changes things from one thing to another. But the Necromancy spells do all of these different things whilst merely laying on a flavor or theming of "death". It doesn't matter what the spell does... if it has a death or undeath flavor to the spell it becomes Necromancy. Which is really why it should be considered one of the "thematic" types.
After all... a pyrokineticist's fire spells can protect the caster via fire shields (abjuration), can blast creatures (evocation), can create animals, objects and walls out of fire (conjuration) and so forth. While the Necromancer can influence your mind to cause fear (enchantment), can animate dead bodies (transmutation), can shoot negative energy (evocation), can gather information by speaking with the dead (divination), can protect themself with a necromatic facsimile of life as a health shield (abjuration) etc. etc. So long as the flavor of the spell is death or undeath, the magic can do anything at all. Which is thematic rather than stylistic. But that's just me.
