DS1 was 3.1 kg at birth and was nearly 7 kg by 3 months. Over 9kg by 6 months. DS2 is almost identical on his growth charts. It was never suggested that I should reduce feeds, my paed was really impressed that my boys were gaining like that when they were BF.
Ignore the advice, it is bad advice. If you and bubs are happy then keep doing exactly what you are doing.