I think there were a lot of things which seemed overpowered until you actually put them into play, which a lot of people didn't.
For instance, the Battle Blessing feat from Complete Champion seemed like it was wildly overpowered, as it let paladins cast any spell on their spell list with a casting time of 1 standard action as a swift action (and cast any spell with a full-round action as a standard action), essentially letting them use Quicken Spell on all of their spells with no level adjustment. Crazy overpowered, right?
Actually no, as it turns out. You see, paladin spellcasting in 3.5 was ridiculously weak for several reasons. For instance, their caster level was half of their class level, which meant that it became progressively more difficult to get past enemies' spell resistance as you gained levels. Likewise, their spellcasting was Wisdom-based; paladins already needed a high Strength and Constitution to be front-line combatants, and Charisma for a significant number of their class abilities, which meant that they tended to tank Wisdom, meaning that their spell DCs tended to suck. And of course, their reduced spell progression meant that they were casting spells like dispel evil at 14th level while the party cleric had gotten it back at 9th level.
All that Battle Blessing really did was let paladins use buffs and supplementary healing without having to give up their full attack actions, which was an overall minor increase in their power by making what was effectively a worthless ability (i.e. their spellcasting) slightly less worthless. In other words, it was a minor band-aid of a patch in the form of a feat, rather than being the massive boost in power is appeared to be at first glance.