My favorite example of "thoroughly bungled idea" is a WarShip: the Sovetskii Soyuz. The Soyuz was the product of a cruiser arms race touched off by the Lyrans introducing the Tharkad-class. The Star League spent 50 years looking at the Tharkad and asking themselves "how do we beat this?"
The answer was to design a Heavy Cruiser that was slower, more poorly armored, more lightly armed, had no point defenses, carried half the fighter compliment and had two fewer drop collars.