It's been often stated, but I'll say it again: most of the really powerful stuff is in core. Most splatbook material is actually rather weaker than core in general, with a few exceptions (ToB, Complete Champion). Stuff that's objectively better than the average level of Core stuff is fairly rare, and generally peaks out well below the best of Core stuff.

The only reason splatbook stuff can seem better is because players tend to only choose the stuff that's decent, and because they'll choose the stuff that synergizes with what they already have from core.

For example, a Druid will Wildshape into a Fleshraker - is this OP because Fleshrakers are OP, or because Wildshape is OP? Or is it a bit of both?

For another example, a Barbarian ubercharger does a couple hundred points of damage in a single round - is this because Power Attack is OP, because Shock Trooper is OP, because Leap Attack is OP, or because Rage is OP? Or do a lot of strong pieces add up to something impressive?


In general, powercreep is a myth. There's certainly the occasional "fix" like Tome of Battle that brings melee types closer in line with spellcasters, and there's certainly the occasional poorly edited/tested book like Complete Champion that throw a bunch of stuff at the wall to see what sticks (I generally encourage ToB and ban Champion), but those are the exceptions. Splatbooks are generally on the weaker side, not the stronger side.