Why would you want to REDUCE someone's stats, especially if they're already playing and enjoying the character?
These people aren't competing directly with each other. In a cooperative game, complaints based on overpower/underpower are simply jealousy and spotlight-envy. And, to be honest, having played a cleric for 10 levels, anyone envying the cleric's spotlight has got to be kidding themselves.
Sure, you can make a War/Strength cleric that tears it up in combat. The thing about that is that that's what that cleric is made for. He won't be as good at other things as a cleric with, say, the Divination/Magic domains, which will be comparable in arcane knowledge (not spells, but knowledge) with a wizard. That Divinatory cleric won't be as good at subtle manipulation as a cleric with Trickery and Travel. In NO way do these clerics replace other group members, because being a cleric comes down to one thing: Healing.
Domain spell slots aside, the VAST majority of my cleric's spells were swapped out for healing. It's just expected, and you can do it, and healing is most likely the most efficient way of adding to the effectiveness of your party out of ALL the neat spells you can do. Sure, a cleric can swing a mace around, but most will spend the early rounds of combat buffing and the late rounds healing, and if the cleric's any good, the combat won't last very long.
The cleric is very flexible on paper, and that gives the illusion of power. On the other hand, no one cleric can do ALL of that. Consider the restrictions of alignment, adherence to the gawd's tenets, and other roleplaying restrictions, too.
Rogues depend greatly on their skills, but they're FEARSOME with the right ones. A rogue with Gather Information can be almost as good a diviner as a Diviner. A rogue with good stealth skills, tumbling, and Spring Attack/Mobility can be a terror on the battlefield. Improved Initiative will give a rogue tons of great chances for Sneak Attacks, which is where rogues shine. Not to mention that they can all use magical devices, detect traps with Search, and have enough points to keep Pick Lock and Disable Device high, whereas no one else does. If your rogue is having spotlight envy, then something's wrong.
The best guage I know of for overpoweredness is how often people want to play the class. I usually run the party's cleric as an NPC beause everyone seems to want to be a melee class or rogue in our group. That says something to me. Maybe the 3E cleric's power and flexibility is payback for people who want to play such a support class in the first place.