Definitely the mastiff needs putting right one of the oldest breeds so the first on the hit list for KC standards.
I too have been around this breed and the fittest old English mastiff I saw resembled a great Dane but was a ped he made 11 I think that was due to keeping the weight off by plenty of exercise and running had the most amazing good temperament unless he was attacked by other dogs ( which happened a lot) most would run in all aggressive and he would just stand still and most would stop and turn tail lol the really stupid ones would be pinned down by the throat until it calmed