I disagree. He has always been excellent from the beginning of his Youtube career. Maximum potential skill levels and skill acquisition/growth rates vary from person to person. I think most people wouldn't have as much success even with twice as many hours invested in the 4 separate crafts (!) of mathematics communication, data visualization, video animation, and video editing. I know I wouldn't, and I consider technical communication one of my strong suits.

Everyone can improve with practice, but some people really are gifted.