Some programmers are gardeners. It sounds like you're one too. Your job is to maintain a large existing codebase. You probably didn't understand the entire codebase before AI, nobody did, so it doesn't matter that you don't understand it now. AI is very good at gardening, nobody doubts that.
Other programmers are painters. Their job is to start with a blank canvas and create something that others will value. When AI tries to paint, it tends to produce slop: a facsimile of everything it's ever seen.