[SixOfSpades]

In my book, Multiclasses are more powerful than their respective Dual-classes, simply because of HLAs. Take the Ranger/Cleric: It gains HLAs only a little slower than the Ranger->Cleric (two classes, each levels up half as fast, and Rangers are slower than Clerics), but each time, you get to choose from either pool. So, while the Ranger->Cleric is choosing things like Earth Elemental Transformation and Mass Raise Dead (and, after they've already been chosen, nothing at all), the Ranger/Cleric is chalking up some more Hardinesses and Greater Whirlwinds.

Multiclasses are always at the top of their form. None of this "now we have to drag Jan along while we wait for my Level 25 Assassin to reactivate."

True, some of the kits, especially in combination with other classes, are insanely powerful: Kensai-Mage, Kensai->Thief, and Swashbuckler->Fighter are just plain nutso. But when you consider that Dualing means you must be Human, whereas Multiclasses must be demihuman, you soon realize that you're taking a kit and sacrificing good Saving Throws.