Are you saying that they are getting numbers in tackles and deliberately not putting the player to ground?
Was this all game, or just that period after half time? I'll re-watch and check it out.
Could be just related again to the Sharks not having compressed defence because the Souths sets started farther out, but I'd have to see the instances you are talking about to comment.
Defensively you would usually cover only ~60% of width the field when a team is coming off their own line, 80% when they reach half way, and 100% when defending your line. If a team starts a set on their 30 they won't be facing as many defenders as they would if they are coming off their 10.
It should be impossible to go through a team from inside your own end. The compressed defence is daring you to try to take risks and go around them.