Since most won't actually deal with fintech (I don't know the stats on HN, but I'm talking devs as one industry), your first "a" example might actually be better than your first "b" example, depending on the complexity of the software. In lots (probably most) of industries, having a good codebase would mean architecture decisions were solid, but the domain/service layer is bad. Maybe my experiences don't match most of the HN crowd, but usually I get stuck with very detailed domain/service rules, but the architecture is a problem where too much memory or CPU is being used, just to abstract away the actual rules of the application (the purpose). Usually when I've been brought in to rebuild an application, the client is fine with the results, but they are upset over performance and/or cost to run the application. For anything of actual complexity, it's usually the supporting code that is the biggest failure, because complex apps usually have decent requirements. Now, if the requirements were bad, and the architecture was bad, AND the domain/service layer is bad, I don't know if there's anything to fix that.

"Perfectly implements" is doing a lot of work there. Enterprise software is very rarely perfect out of the box, and the issue with bad code is that it can make it extraordinarily hard to solve simple problems. I have personally seen tech-debt induced scenarios where "I want a new API to edit this field in an object" and "Let's do a dependency upgrade" respectively became multi-month projects.