Everyone's pretty much hit the nail on the head in regards to what makes our defense so good. From getting as many bodies into the tackle as possible, to holding the player still before usually placing them on their back, and if possible facing their own try line. That coupled with the fact that we peel away from the tackle one at a time, all contributes greatly to slowing down the opposition's PTB.
A consequence of those tactics though are the extreme amount of energy it saps from are players. It's near impossible to keep that tactic up for eighty minutes week in week out. That's why IMO we do on occasions suffer from losing large leads.