Yokoyama's supervising/corrections have really improved.
I think the Uchiyama episodes started to stand out more - in a bad way - because the art evolved and was getting more detailed, except his episodes, that remained pretty much the same all the way through GT.
Still, the animation for his episodes did get better too. Piccolo vs 17 and his Buu arc efforts come to mind.
Yeah, that was part of it. Uchiyama was the one supervisor to really maintain the early arcs' style, but what really killed the look of his episodes was the fact that he went from four named key animators on his episodes to just two. Before the Artificial Human arc he rarely if ever did key animation himself…then he had to when
was the only key animator that didn't jump ship. When an episode is only key animated by two people, one of them being the supervisor and an awful key animator… .