The Z28 is also much more expensive than the more powerful ZL1. The road race cars are built for something different than the higher hp models. The amount of money that went into the brakes, the suspension, the chassis, the NA drivetrain, the wheels, etc. is very great in comparison to just adding power.
526 isn't the most they could've possibly gotten, it's what they chose to stick with for the best balance for the car's purpose. It will be faster around the road course than likely anything under $100K. I understand that this car doesn't make sense for your goals, but you have to be willing to accept the fact that Ford built a car for a different group of enthusiasts. It doesn't mean that they don't know what they're doing.
I think comparing a Z28 and a ZL1 is a bad comparison. ZL1 is a much better all around vehicle. Z28 is much to track oriented to be daily driven.