To my opinion it is more individuals than breeds. Aby Filou is his 6,5 or 7 lb since he is 14 months old, he's 6 years now. Tigris is 13 lb since he is adult -he's also 6. Tigris bones are longer and bigger than Filou's and he is close to overweight but ok.
If you look at Vio&Juni's Juni she is a slim tabby and I am sure she will stay like that.
Cats like European shorthair, British shorthair or some other genes are bigger than Abys or Russian Blues but all of them are overweight if they eat too much. (If you look at humans it's similar: you can be overweight with any skin or hair colour).