Are wizards powerful? sure. The key is to avoid wizards being the equivalent of Gandalf while the rest of the party is the equivalent of the thirteen dwarves from the Hobbit. And that level of power disparity should not happen if the melee classes and the wizard classes are approximately the same level.
I don't recommend changing the class. I prefer in game solutions.
My role-playing suggestions:
1)If one player is dominating combat, make the other players the focus of role-playing. Involve them in the role-playing by making them related to an NPC or the center of the quest.
2) If a combat is over fast, that means more time for role-playing.
3) If wizards mass-producing magical items is an issue, control the amount of time available in the adventure for item creation.
My tactical suggestions:
1) After every rest, ask the wizard player for a copy of his written list of memorized spells. You'll have a copy behind the DM screen. That will reduce the wizard's versatility.
2) Enforce spell components, verbal, and somatic gestures. No spell casting while swimming, bound and tied, silenced, etc.
3) If the NPCs know that the wizard is the most powerful member of the party, have them target the wizard. Imagine this is american football, the wizard is the quarterback, and the defense wants to sack the quarterback.
4) Use anti-magic field (Beholders), spell immune creatures (golems), and spell resistance creatures (DRAGONS).
5) Throw more powerful opponents at the party (EL+4, etc.).
6) Use outer planar adventures with different planar qualities.
7) Use opponents who are even more powerful than EL+4, but have a special weakness. i.e. an EL+10 opponent, who can be defeated by a special weapon wielded by one of the non-wizard characters. The other party members have to help distract and defend the wielder while the wielder destroys the BBEG.
8) Worst case scenario: use Wizards (possibly with templates) as BBEGs
