The disadvantages of duplication are greatly reduced in the world of AI. From my experience it can easily detect the duplicates and refactor code safely. On the other hand, code without abstractions is easier to read and easier for AI.
With AI, we really need to rethink the clean code principles.
Seems to me like the last thing you want to do is worry whether the LLM has a large enough context window to keep an eye on all duplicates. So I'd argue to deduplicate directly, where possible.
Personally I've seen way more duplication as a result of AI in large codebases