I think the magic system should be changed to be more like the research system, and made more separate from the worldly tech system.

For instance currently magic is a tech tree, which unlocks the spell books, but the arcane research unlocks the generic spell levels, and you can research any spell from any spell book you upto the generic spell level you have learnt.

As a direct result you are encouraged to cherry pick the spells from all the different books you have unlocked, with little incentive to focus on a single school, unless you gather multiple shards of that type.

I believe the magic research system should be divided into a series of books, almost analogous to the current tech system, but instead of each technology having prerequisite(s) each spell would require a certain level in its spellbook.

For example the arcane study screen would contain several spell books, which could be something like this:

The spellbook, Ignum (Fire), at level 0, could contain the following spells:

Creo Ignum, a single target damage spell that fires a bolt of fire,

Lore of Fire, an enchantment adding fire damage to a units melee attacks and allowing this enchantment to be added to created items,

Forge of Avernum, a city enchantment increasing metal production.

Learning any spell in the book would increase the level of the book, and increase the level of spells available to be learnt.

The same spellbook could contain say;

Creo Ignis Mare, a level 2 spell, could be an area of effect version of Creo Ignum, but would require you to have learnt at least two other fire spells before you could research it.

This model would make spell casting more themed and less, well random feeling as it is now.

I also believe the spells should be made more distinctive, perhaps each book should have a particular "trick" associated with it, for instance fire damage spells could add dots, earth have the highest instant damage, air the largest aoes and range, water could add debuffs or perhaps move the targets.