Suggest Cumbria1 reads Dick Huddarts piece in the Whitehaven News last week.
Huddart is widely recognized as one of the greatest pack players in the game, but by his own recognition he was a line buster, not a tackler.
Different pack members have different attributes, no forwards put in 40 tackles per game, bust the line regularly, offload at will, play the ball at speed, support half breaks etc. etc.
Bull executes his role in the pack very well indeed. For example his carry the balls may not be regular line busters, but he doesn't half pull in the defensive tacklers being such a big man AND he carries the ball in so often during a game that he is an absolute nightmare for the opposition defense, sapping their energy throughout the game. Bull is an excellent example of a prop doing what he does very well.........carry in, tackle, play the ball at speed, back up and draw in tacklers / draw down opposition energy.