I also don't like it how everything is random and you can go through entire game without acquiring other spells, I was very lucky to get ice snake besides fireball, although I would prefer lightning, meteor shower, acid rain and other I've never even heard of.

oh yea, that is the crux of the matter. your unit power increases over time as you gain levels and leadership. Your buffs/debuffs, once leveled, also increase in power, because they are percentage based. A phantom spell now creates twice as many griffins for me as it did when i first got it, because my stack has twice as many griffins in it. they require X mana for Y% improvement / weakening. So they remain as useful.

Your direct damage spells depend on luck and have a distinct "level" that it does not progress beyond... fireball absolutely dominated the battlefield for me at levels 5 and below. It was a one shot kill, sometimes killing multiple enemies with one shot.

If you get LUCKY and get an attack spell many level beyond you, go ahead and make the most of it until it becomes obsolete. Just don't spend too many crystals leveling too many attack spells.

Another thing is, a lot of the direct damage spells are NOT chaos magic. only the fire ones, and all the strong enemies are immune to fire (but not to physical or cold... so your non chaos magic direct damage remains effective)