Rica Matsumoto told in an interview for Anipedia magazine, that the fat pervert Tetsuo Yajima (God of the Ash self-inserters) told her "I want to create a cool Ash that everyone will look up to". The problem with this is that Yajima defecated on Ash's essence and personality, turning him into an artificial, boring and bland bot shonen character. This surely also had repercussions, as to further enhance the figure of the new Ash, Serena was turned into an object of desire for the male audience who were obviously going to self insert themselves into the new Ash. Serena ended up as a female character without dignity, who crawls around like a worm and whose existence and popularity depends solely on Ash.
While Ash self-inserters existed before, XY multiplied them by millions by offering a Gary Stu Ash. Today we are still suffering from the aftermath of that series for kids with no self-esteem. After XY, fortunately Tetsuo Yajima would be removed from the management of Anipoke and his nefarious "legacy" would be erased in Alola.