An attempt to explain the weight distribution by grouping dogs as pet vs working breed and less athletic vs more athletic would probably be somewhat more successful (fair fit).
ɐn ɐtˈɛmpt tʊ ɛksplˈeɪn ðə wˈeɪt dˌɪstɹɪbjˈuːʃən baɪ ɡɹˈuːpɪŋ dˈɑːɡz æz pˈɛt vˌiːˈɛs wˈɜːkɪŋ bɹˈiːd ænd lˈɛs æθlˈɛɾɪk vˌiːˈɛs mˈoːɹ æθlˈɛɾɪk wʊd pɹˈɑːbəbli biː sˈʌmwʌt mˈoːɹ səksˈɛsfəl fˈɛɹ fˈɪt.