You're underestimating the amount of effort put into simplifying and clarifying implementations, APIs, and documentation.

This doesn't imply that preceding implementers are unskilled. Part of this improvement is hindsight, but a not-insignificant part is Python's flexibility.

I can vouch for the apparently unbelievable productivity gains but I'm just not sure how to prove them!

Edit: As for not sharing these gains -- that's part of the point of this post to the official PayPal engineering blog :)