Well its an obvious insight. But the actual increase in time spent on page is what would be interesting.

We have the session lengths in terms of time as well -- all the data is on git

But you had the gamification stuff in place for everyone right? So there'd be no control group.

i cant respond to your note directly, but true, a further experiment could be done to analyze how much of an effect the gamification had, but the existence of the effect is clear