Is this really any different from debugging code that has been built by hundreds of people over 10s of years and you're just the latest schmuck working on it?
It really depends on if the 10-year-old code in question was put together by a talented team with high standards, doesn't it?
But regardless, on a large project, you're always going to have some version of this problem. At least when you yourself are getting in there and writing and understand the code, you have a half-decent shot at debugging in a reasonable period of time. When even you are vibe coding your additions to the pile, you're all the way back at square one when shit hits the fan, trying to learn it all from scratch.
Maintaining legacy code built by a huge team over decades is sort of famously difficult and the productivity expectations on those teams is incredibly low. A project getting into a similar state after only months would be disastrously bad.
