Type diversity is when a type specialist doesn't use 2-3 Pokemon from the same family line, Pokemon not associated with their type, and Pokemon who are already taken as someone else's ace Pokemon. I used Glacia as an example, because she's one of those type specialists who ruins type diversity, and it's important that her two Sealos and one of her two Glalies need to be replaced by different Ice types for the sake of type diversity. GF managed to fix Flint's team in Platinum, as well as Candice and Volkner's team, so why not the Hoenn gym leaders and Elite Four members. It furiates me when they only change their team post-game in remakes, when I want their teams changed from the get-go to bring type diversity justice.