Adding in school passives that are only accessible by the specific school from the start of the game could give every school a stronger position.
For example Ice gets an aura indicator to show how much damage your team is about to take. Red being the most so they know who to focus defenses on for that round.
Myth have full control over their minion's spell casts. Or even make their minion stand with them like a second pet that gives a specific stat buff (resist, pierce, damage)
Life applies a Spirit Shield equal to the amount of pips spent on their last heal (rebirth applies 700hp shield to all allies balanced by removing the original shielding). A Fairy will apply a 200hp shield to the target.
Making these passives PvE only will give every School a reason to be played apart from favourtism because let's be real. Ice is overshadowed by Death in terms of defending a team from damage and Myth's utility is wasted by it working against them because the minion uses low damage spells to break your setups.
Also in general, make ice taunt aoe cast to all and not each individually.