i dont know where you see weight pulls but we go to alot of ADBA shows and its all game bred type pitbulls , they are id say better meant for weightpull then most bullys out there, although both if conditioned can do well in that sport. but to answer your question i believe game breds were doing it before bullys were.
While the ABKC has sanctioned weight pulling there aren't many dogs that compete (it was only sanctioned a few months ago), at least on the East Coast so I am not sure what you are looking at on Youtube. I have only seen APBTs in WP to be they honest. I am sure a few Am Bullies can pull, but they are few and far between. BTW there are no "bully type pit bulls." There are American Bullies and there are APBTs. Pet peeve of mine