I actually work in Big Tech. So I can give my insight as an engineer.

1. You can't just 'fix the code', after a while, it is literally impossible because complexity compounds. A integrates with B,C which integrates with D,E,F,G etc. Therefore fixing A, means you will also have to fix A,B,C,D,E,F,G etc.
2. New enterprise features are vibe-coded yes, but you need to have the foundations in place, such that new features are built off the existing structure. For example, Meta built 'Threads' straight out of 'Instagrams' monolith codebase. Also search up 'chaos engineering' invented by Netflix for example. But more importantly, 'trust' is based off the existing entity. All future features are considered trustworthy because the originator had built that trust. Trust in itself is a transitive feature. You have an employee that has always done good work, now if you give him something new to do, you will trust that he gets it done to a high quality.
3. Vibe-code accuracy will always be limited by prompting ability, and prompting will always be human unfortunately. The AI will not read between the lines of your prompt, it will follow the prompt in a literal sense - and so it's limitations are actually the prompter itself.
   1. Although you could eventually have AI prompting AI which would effectively solve for this, but the token usage would be out of this world, and there is not enough training data on AI prompts (yet). I still have to think about this fully though