My personal opinion is that the big gains in programming productivity in large projects have have to do with how code is organized and structured. The right abstractions are also key to keep the inherent complexity under control. It is not about implementing x feature in t time. It is more about implementing the feature in a coherent way, and the gain is long term. To measure and compare that, you would need to track 2 projects implementing the same features over a period of time. That experiment is hard to do.