Magic will easily change the balance of a fight in your favour if you use it right, but some magic is better at this than others. Metal for example is pretty balanced at the moment. Metal doesn't bring as much utility as Life or as much damage output as Shadow but it does what it does very well, post the buffs mind you.

But this is all subjective, whilst I personally rather like Metal magic someone else won't. There's also some magic which is just not very useful like the Lore of Heavens which is almost certainly the weakest lore at the moment.

Anyway rambling aside magic isn't meant to be so powerful that it will automatically win you a game and it's best used on large size battles since that is the unit size that CA has balanced everything in the game around. If you decide to play with small armies, some Magic will do a lot of damages and others will just hit nothing. If you play with ultra armies you'll find magic just doesn't have a big enough aoe size and that some targets have way too much health.

So TL:DR what you should get from this is that magic is very useful but only if you play with large unit sizes, with the right lores and if you use the right spells for the situation. If you don't, magic will seem pretty lackluster to you.