I have a more magic centred addition to this guide.

[url=http://tvtropes.org/pmwiki/pmwiki.php/Main/LinearWarriorsQuadraticWizards]

"A quirk some Video Game and Tabletop RPG game systems share is that melee classes are more powerful, versatile or useful at lower levels than casters or magic using classes. However, the trend reverses at higher levels, when the magic users gain a breadth of both versatility and pure power over simplistic hack and slash heroes."

In brief, magic users can easily get much more powerful than they should be. Their increase in power in relation to experience accelerates as they get more experience, as they get not only stronger but also have more powerful and diverse spells at their disposal. This is in contrast to other means of combat, such as melee combatants, where their strength progresses more or less evenly, especially since they don't have the versatility of magic users and face physical limitations. Magic, on the other hand, is there to overcome physical limitations.

On the flip side, early on magic users are typically weaker than warriors as their powers are not useful until they are well-trained. However, early on warriors have the upper hand as it doesn't take much training to bash up your enemies.

A way to counter the disproportionate increase in magical power is to put some kind of limitation on it, such as limited power (often 'mana') or some physical or mental cost of using magic. Care needs to be taken there to avoid nerfing wizards too much, otherwise the scales may tip the other way and they may become effectively useless.