But any abstraction ends up with a signature and a name that can quickly be found in code.

The risk of a long-lived duplication losing its shape and being hard to find is much greater. Especially if the code is going through multiple hands.

I once had to pick up a project — a working, fully functional website. I could see, pretty clearly, the work of several people. All but one of them terrible.

The one was a diligent developer who was fully wrong in their abstraction (in fact significantly) but was consistent in how they used it.

The rest had simply worked around that code, copied and re-copied their own modified duplications and let things lose any shape. The result was error-prone stuff.

Clearly either the budget (or the client's capriciousness — a separate issue and arguably the bigger one) scared away the one guy, who I actually wanted to talk to but could not track down. He possibly had the origin story, and I wanted to know why his particular abstraction, which was at odds with the framework, was there. It was good code in the wrong shape, and it clearly used to do more, and that is interesting.

All the expedient people who had decided to avoid his code and just patch in duplicated pieces around it were the problem. There was no form to their solution at all. And that had clearly happened over some time (because you could see several different code styles)