Wizards are just fine the way they are. They are neither overpowered nor underpowered. Dangerous? Sure. Vulnerable? Sure, especially at low levels. But consider that, at low levels, they also have access to some of the best defenses and attacks. And I can assure you, a 25th level paladin wielding a Holy Avenger versus an evil Outsider? Not Pretty. No spellcaster in my game has EVER done in excess of 300 points of damage in one round...but the paladin has, and the arcane archer routinely does between 150-200 points of damage against the right kinds of targets.
Where the wizard excels is at being able to compensate for any kind of enemy. Tough melee character? Dominate, Dance or Enfeeble him. Undead? Disintegrate him. Enemy Spell Caster? Exhaust, Idiocize or Enervate him, among dozens of options. Need a breather? Maze somebody.
And as was mentioned above, availability of level-appropriate spells doesn't translate into more kill-power. Utlity, yes, but violent power? No.