I think the show, as a whole, has been shifted severely to entertain the younger audiences. If you watch the Kanto episodes the diction was, to some degree, very sarcastic and witty as well as inspirational. In the newer episodes the diction has been "dumbed down" to appeal to the newer generation of children. Also, I think another thing that makes the obvious personality separation between Kanto and Unova Ash is his voice. It is if when they changed his voice, they also changed his personality. I found the Kanto Ash to be much more appealing than the Ash we watch today. That's just my opinion though.