This sort of system only works with internal software and an unusual amount of data. If we were in the business of selling that software we could not have charged a higher price for the new version over the old, the tweak could only be unlocked because we were able to control staff hiring and staff onboarding fully to make use of the new changes.
As part of the aquisition I got access to their previous codebase which was some sort of incomprehensible PHP monolith, with the persons who wrote that code long gone. Thanks to LLMs I was actually able to extract the core useful concepts (again, sufficiently deep domain knowledge that I knew exactly what to look for). Without LLMs i would have probably extracted the absolute minimum and let the rest rot.
There is no reason a dev of comparable skill and domain knowledge would not be able to do that for what I built here.
By that point it might no longer matter though, but I suspect that such code would have a lot more exposed edge cases than one where someone actually thought things through before coding.