
Logistics will give you an advantage in resources, artifacts, and levels, yes. But they didn't mention that with Skilled Education, the level advantage translates into a huge advantage in stats. You can ask those who play online often – how do they feel about, say, an Argath with a Logistics specialization? The answer is clear: it's hard to outpace her, both in levels and just on the map.

Now, about having two schools of magic.
"You won't have time to cast everything in battle" – that's a silly statement. You need to combine the schools of magic so that you can cast spells.
Specifically – the Necromancer. Darkness + Summoning is an excellent choice. At the beginning of the battle, mass-cast spells. Especially – Mass Slow. And then you can summon Fire Elementals. And Phoenixes. And even put a Shield on Zombies.
For example, my Leto used to summon Phoenixes and put Vampirism on them after switching to "necromancy schools of magic." And that created an unkillable, high-initiative damage-dealing unit...
So, having two schools of magic is more of a norm than an exception for spellcasters.
Горящие реки сходили с ума, пытаясь остаться водой,
Земля пропустила коварный удар, раскрывшись на шаге вперёд,
Взлетел разъярённым драконом Огонь и понял, что тоже умрёт...