A bad design may work equally well when compared to a good design, given it's patched enough.

Totally disagree. A bad design can pass all tests and appear high quality, then crumble under high load. Even quality is subjective. Most people would assume it means being good at every aspect, but passing tests doesn't not guarantee that.

Unless the bug fixes are so fragile and/or convoluted they make any change in business requirements almost impossible to implement.