English Mastiff’s aren’t stupid at all. They are lazy. That isn’t the same thing.
My dog knows when my wife gets out of bed he can climb up and sleep with me. (I work shift work.) When she is home he sleeps in his dog bed. He just has little interest in exerting himself for anything other than hanging around me.
I think they forgot what the dogs were designed for.
My next door neighbors have 2 English Mastiffs and have had a series of others, according to them they are the dumbest breed around. The wife would like to have a different breed but her husband won’t hear of it.
Maybe your is an exception, because they have had about 5 in the last 15 years.