No, its not.
> It's uncanny rewatching movies where the fat kid everyone picked on then would be on the average to skinny side today.
The distribution of body types in film (in the 1980s and otherwise) represents the fashions of the motion picture industry, not (except coincidentally) broader society. The relation of that fashion to broader society is very much not consistent.
> Forget being transgendered the majority of the US would look barely human to anyone from the 80s.
Being an actual person from the 1980s (70s, in fact) I can say with some confidence that this is not true.