Excellent summary but I have to take two exceptions:
The Lore of Fire is certainly mediocre, but a low to very-low point games (500-1250, the ones that brand new players reading this guide will play) the Lore of Fire is excellent and has several important advantages: Low casting costs, the Kindleflame trait gives a big boost to low level casters, and the Fireball spell is a guaranteed Flaming ranged attack that can duplicate the power of a 10-elf archer unit. Extremely useful if you've got just one low level caster, slap a Silver Wand on and the Kindleflame helps cast both spells the wizard will have!
Second, the Lore of Light. Excellent but exactly the opposite. It requires a tailored build at high points level, but a group of four Light mages (1 lvl 4 and 3 lvl1, or 2 lvl one and a Prince with the Crown of Hoeth) can wreck massive havoc. First, Banishment is the base spell so every mage can have it. With 4 mages that's D6 S7 flaming attacks from each of them! Killer vs. war machines, monsters, monstrous infantry, characters, and beasts. Well, to be honest nothing likes 4D6 S7 Flaming attacks, and forget about demons and Undead! Or you can have fewer Banishments and all the remaining Lore to cast. I10 is not as awesome as it could be, but it is great against Dark Elves, Skaven, and characters.
Your second paragraph is horribly inaccurate. Banishment is the 5th spell (discarding the sig), so everyone has to try to roll for it. Plus if you are running the way you even plan on it, you only ever get it once, as the rules say if a spell is taken by one wizard you cannot have it a second time beyond two expections:
1. all the spells are already known (like Master of Sorcery), or
2. you are taking the signature spell so everyone can know it.
Tyranids-Hive Fleet Hydrus(0/0/0)
WoC-The Host of Alctheus(0/0/0)