In every depiction of Maui I've ever seen prior to this movie (going back as far as kindergarten), whether you're talking about books, paintings or centuries old traditional carvings, Maui has been shown with a a slim/athletic build, somewhat similar to a swimmers physique. The majority of complaints aren't from fatties getting triggered because a cartoon character looks like a hippo. It's because  "fat Maui" is entirely a creation of Disney. It's a lousy character design because it pays no regard to 1000 years of prior art. I understand that Maui may mean nothing to you personally, but to people who consider the character to be part of their heritage, it's like portraying Jesus with a handlebar mustache and a top hat, or Moses as a tranvestite.