Be careful with what you mean by "keeps improving." I think I know what you mean, but Canelo just gets sharper at what he has already been good at. His deficiencies have not abated. I also don't think that anyone was saying that GGG requires a new dimension to his game. GGG's opportunity lies in his willingness to go back to that amateur background more than anything else. This may sound counter-intuitive but I am in no way mistaken here. GGG looked worse when he tried to brawl Canelo, but he was actualy out-boxing him for large stretches. His silver medal in the Olympics and hundreds of amateur fights get undervalued because he is willing to take a punch and is aggressive, but I encourage next time you re-watch the fight to see how cleanly they hit each other. GGG can get hit, but he doesn't often get hit as cleanly as people think. Just as Jake LaMotta, a man renowned for his chin, was not hit as cleanly and as often as people think. I am not saying that Golovkin is some savant slickster like Pernell Whitaker, but I am saying that just as some pure boxers get criticized for being a soft touch, so too, do some pressure fighters - like Golovkin - get unfairly reduced to being paleolithic brawlers.
The inverse trajectories are a matter of physical decline for Golovkin and improving experience for Canelo, but the approach in the ring allows for "improved performance." Just look at Leo Santa Cruz's rematch to Frampton. A close first fight, but then LSC made some adjustments. He didn't all of a sudden become someone else entirely, he just fought behind a jab and took a step back to remove himself as a target (if you watched the fight, Frampton would catch LSC on that first step in, so LSC took that away by making small steps).
Sorry for the rant. I'm on a roll today lol.