I'm not some DRY zealot, but I've been in the "this system needs really similar changes to a ton of geographically distant code for simple changes" salt mines a lot. The people who say that kind of spaghetti is unavoidable are just as wrong as the ones who say it can only be fixed with a grand rearchitecture by a rockstar.
If you spend a lot of time performing monotonic tasks, then your organisation needs to delete and refactor for a while until change in 'hot' areas of the code base are easy to make. Reaching for some code synthesis SaaS to paper it over will worsen the problem and should result in excommunication from the guild.
My current codebase is ~3 million LoC all in all (not greenfield, really old code), working on it by myself, the complexity is definitely manageable between Claude and me :)