There is a difference between interpolation, which the majority of humans are performing daily with coding in private codebases, and genuine extrapolation, which is difficult to prove and difficult to find in high dimensional spaces. LLMs may not be able to easily extrapolate (and when it does it's due to high temperature), but they can interpolate extremely well, and most human growth and innovation today comes from novel interpolations, which are what LLMs are excellent at.