Yet, at no point during this development did any project leap forward by a huge margin. Instead, every paper built upon the last one by making minor improvements and increasing the compute involved. Since these minor improvements nonetheless happened rapidly, the result is that the GANs followed a fast development relative to the lifetimes of humans.

Does anyone have time series data on the effectiveness of Go-playing AI? Does that similarly follow a gradual trend?

AlphaGo seems much closer to "one project leaps forward by a huge margin." But maybe I'm mistaken about how big an improvement AlpahGo was over previous Go AIs.