Nargott
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Chaos isn't needed for survival, but to kill. The point is that while you're setting all this up, a combat-focused hero might manage to destroy a large part of the army (each cast takes up 100% of the turn, not 50%), so physically, even such powerful casts might not be enough to kill the remaining troops. But to last longer while the hero uses Chaos/Summoning – that's possible.
I just don't see any reason why this shouldn't work. You invest only 4 perks in Light/Dark (basic Light + Defense Master, basic Dark + Mind Master), and you already have powerful containment tools; it's not necessary to maximize Light/Dark, you can invest the rest in other schools of magic, education, and enchantment.
For example, here's a 15th-level Archmage (shown on the original skill tree):
If you compare this to a similar build focused on solo Summoning and combat skills (Skilled Defense + Dodge + Sturdy Defense + Resilience), the player using 4 schools gets, instead of a base defense, a +6/+6 passive bonus to Magic and Knowledge (equivalent to +12/+12 in the original), and many additional strong options (namely, the Light and Dark casts themselves, and stunning lightning).
I just don't see any reason why this shouldn't work. You invest only 4 perks in Light/Dark (basic Light + Defense Master, basic Dark + Mind Master), and you already have powerful containment tools; it's not necessary to maximize Light/Dark, you can invest the rest in other schools of magic, education, and enchantment.
For example, here's a 15th-level Archmage (shown on the original skill tree):
If you compare this to a similar build focused on solo Summoning and combat skills (Skilled Defense + Dodge + Sturdy Defense + Resilience), the player using 4 schools gets, instead of a base defense, a +6/+6 passive bonus to Magic and Knowledge (equivalent to +12/+12 in the original), and many additional strong options (namely, the Light and Dark casts themselves, and stunning lightning).