> We _already_ live in a world where most of us spend much of our time reading and trying to comprehend code written by others from the past.

We also live in a world where people argue endlessly about how we don't need to write documentation or how it's possible to write self documenting code. This is where we spend so much of our time and yet so few actually invest in the efforts to decrease that time.

I bring this up because it's a solution to what you're pointing out as a problem and yet the status quo is to write even messier and harder to understand code (even before AI code). So I'm just saying, humans are really good at shooting themselves in the foot and blaming it on someone else or acting like the bullet came out of nowhere.

  > What's the difference between

More so, I must get misreading because it sounds like you're asking what's the difference between "messy" and "messier"?

If it's the same level of messiness, then sure, it's equal. But in a real world setting there's a continuous transition of people. One doesn't work on code in isolation, quit, and then a new person works on that code also in isolation. So maybe it's not the original authors but rather the original authors are a Ship of Theseus. Your premise isn't entirely accurate and I think the difference matters