I suspect you're trying to apply logic where it doesn't belong. Thinking of the Miura or the Countach as anything other than fantasy machines is a mistake. The Miura was created by Wallace and Dallara on their own initiative and it was basically something they did on their espresso breaks to amuse themselves. Ferrucio Lamborghini wasn't supportive of the project at all, and Gandini was barely 30 years old when he penned the design. Lamborghini had only been an automobile manufacturer for three years when the chassis was displayed at Geneva. Hell, no one even gave a moment's thought as to whether the engine would fit in the car at all.
They made a little over 600 Miuras over the course of eight years. By contrast, FIAT probably made that many cars before lunch on any given day. And this is during a time riddled with political strife, labor union troubles, protests, and changes in ownership. And these cars were being built by hand (by Italians, mind you). They were probably more concerned about keeping the lights on at the factory than anything resembling quality control. And then by the early 70s you have to add the gas crisis to the list of challenges.
Meanwhile the design houses, particularly Pininfarina, Zagato, Bertone, Italdesign Giugiaro and Carrozzeria Ghia, were creating flamboyant designs that gave no thought to usability or practicality. They were literally dream cars, absurd concept machines that had no relationship to the reality of driving them on the road. And that is what the Miura and Countach are—they're ludicrous fantasies come to life that somehow run (occasionally) in spite of themselves. They were huge gambles from a tiny operation struggling to make its name in the world.
And during this period just a few miles down the road you had "real" cars like the Maserati Ghibli and the Ferrari 365 GTB/4 Daytona. Those cars certainly have their idiosyncrasies, but they're far more grounded in reality than... well, anything that ever rolled out of Sant'Agata. Those cars came from well established (albeit small) companies with decades of racing and manufacturing experience, and global distribution besides.
The Countach and the Miura were brain candy, nothing more, and approaching them rationally and trying to measure them against normal cars is a pointless waste of time.
But sweet Jesus, they're lovely.