I don't know if I can agree with him about voice acting, though:
The singers killed it. By that I mean, the character of Baloo became more Phil Harris and less Baloo the bear. Louie Prima’s King Louie was more Louis Prima than anything you’d find in the African setting. George Sanders was more of an actor than a personality, and he offered Shere Khan a character that Milt Kahl was able to build on. Sterling Holloway as Kaa was also more an actor than a personality, and he played what was asked of him. Ollie Johston was able to develop on it.
Animated features try to continue in the same vein. Voices like Robin Williams or David Spade or Eva Gabor are not going to make the animated character better. It’d be more interesting to have unknown voices that are well cast. Peter Pan, Snow White, Bambi and Cinderella. Lady & The Tramp, Alice, Pinocchio are all brilliantly cast features.
Now, it's true that many animated features go overboard with celebrity stunt casting. But I don't think that's what happened in Jungle Book, even if it did have more big-name actors than Disney's other features. All the main actors except Louis Prima are character actors, supporting players, who happened to have really distinctive voices. The casting of Phil Harris, a popular radio personality, is no different than the popular radio personalities Ed Wynn and Jerry Colonna in Alice; George Sanders may have ben better-known than Hans Conreid (Captain Hook), but Hans Conreid was stil a guy who, at the time, was better-known as an onscreen character actor than a voice actor. And when you go into later actors -- well, Robin Williams, Eva Gabor and David Spade wer all well-cast, good choices in my opinion. As are many other people who have done animation voice acting without a lot of background in voice acting.
Celebrity casting is bad when the actor becomes more important than the character, so that the animators are just animating to the actor's personality rather than finding the character. This happens: it happened when Disney re-used Phil Harris in two other movies and just recycled his Baloo character, and it happens a lot with today's non-Pixar animated movies. But there is often a good reason for casting a celebrity, because these are often people who become famous because they're good actors, or have distinctive voices. And you need good actors with distinctive voices in an animated film.
I realize and understand the objections to famous actors taking work away from full-time voice actors. But the other side of this is that many animated features require a different kind of voice acting from the kind that professional voice actors provide. A lot of cartoon voice acting is a little exaggerated and broad, because that's what's required for television and short cartoons. But to sustain that kind of acting over a whole movie can become difficult, especially when the movie has a lot of serious moments. So the ideal thing is often to find an actor with a really good voice who can use his or her own voice, or something close to it, and sound "natural" in a way that traditional cartoon voice acting is not. There's a reason why Disney usually saved the June Foray, Bill Thompson type of actors for smaller or more comic roles ("Squaw no dance! Squaw get-um firewood!") and gave the lead roles to people who might be fairly well-known but weren't necessarily animation pros (like Cliff Edwards, Walter Catlett, and other people that the audience sort of knew at the time).