One of the arguments I hear against Python is that while initially things happen fast, the effect does not scale for large applications. Or that Java/C#'s static type checking makes it more scalable.
I'm curious if you have seen any scalability effects. For example, did the Python teams productivity stay consistent or did it taper off the further into the project you got? Did the C# team's productivity go up over time? Stay constant? Drop?
I'd be really curious to see the time series on the productivity.
With regards to time series...me too! I don't have enough data to make any statistically-backed claims, but anecdotally Django-based sprints do start off with a big bump in velocity, because you're handed a tremendous amount of functionality upfront via the framework itself, Admin CRUD, etc.. Once a team gets moving their velocities tend to stabilize, which is one of the reasons story points and velocities are such powerful estimation and forecasting tools.
That being said, C# teams seem to have larger standard deviations around their mean velocity. One thing I have noticed is that refactors tend to have differing impacts. Major refactor efforts and rearchitecting almost always noticeably hit the C# team's velocity much more so than the impact on the Python group. Having done refactoring and and rearchitecting in both environments, I tend to think it's a function of the syntactical overhead associated with the C# language.