Don't think surface area - think frontal area. You're still reducing the number of things in the slipstream from 3 to 2. And cutting down the intersection drag where they attach to the fuselage. Plus the weight of associated hinges, pushrods, and other hardware...

It's a good theory, but I guess there must be some reason that just about every plane flying still has a conventional tail. There's still plenty of old Bonanzas around!