I'm convinced fat people like this person and a lot of SJW types in general have some sort of disorder where they are incapable of connecting with anyone they can't see in the goddamn mirror. Their fucking brains have damage or malformation where they can't produce sympathy or empathy for anyone Not Like Them™.  Additionally, because they live such loser lives but are too lazy to change them, they want every piece of fiction to be their wish fulfillment fantasy. So as you said, they want fat characters exactly as fat as them with all these other Goldilocks not-too-this-not-too-that conditions for the perfect story to make the fats feel better about themselves without having to spend the energy to actually better themselves. "The fat character is like me. The fat character represents me. The fat character is heaped with success and love and praise. People must do like in the movie and heap me with success and love and praise because The Movie Is Telling Them To."