As someone with years of FAANG experience, reviewing code competently was actually more strenuous than writing it in the first place. In fact, I'd estimate that truly understanding a codebase required a similar time commitment to writing the amount of code in that codebase. So I don't see how unprecedented speedups are possible with a human in the loop unless the reviews are only being skimmed.
The key to productivity and increasing complexity is inventing solid, thoughtfully designed abstractions and building on top of them, not taking shortcuts by way of a code extruder. If code is constantly getting duplicated or falling into the same patterns, figure out how to abstract or encapsulate it.