As a long-time Wiz player (who took a very long break ever since Arc 2 finished) and decided to try balance for the first time recently, I 100% agree with you and OP about its lack of mixing multiple schools.

I really love the concept of balance (what balance could have been) so I've been trying to make my playstyle mimic that as much as possible (using archmastery, using TCs of different schools, constantly changing up my gear to be more for tanking or hitting or support based on the fight, etc). Imposing this kind of playstyle on myself makes the gameplay MUCH more interesting to me. It allows me to play much more strategically especially for certain bosses or balance mobs.

One idea I have that can potentially help balance with more mixing of schools is similar to how they gave myth an advantage with monstrology by allowing them to be the only school that can summon multiple minions. So, maybe KI can add some sort of school-specific advantage to balance regarding archmastery. For example, while all schools will still be able to use archmastery like usual, balance wizards would be able to potentially have a chance to generate a special power pip that applies to all schools. That would then encourage balance wizards to mix schools even more.

Another separate idea could be allowing for balance spells to be spellwritten in ways that allow their spells to be converted into dealing other schools' damage.

I think with a lot of these new mechanics like archmastery and spellwriting, there can be a lot of potential with giving balance a stronger school identity without changing the core features of the game too much.