Rugby League preseasons are about as hard as they get. The average NRL preseason would be a step up from any Rugby preseason, its probably down to a few things.
- The nature of their games require less time working on technical aspects and more time prepping physically. League is about as tough of a sport as you can play, the simplicity of the game amplifies some of the most basic principles of any form of 'rugby', tackle hard, run hard and work hard. Props don't need to scrum, locks don't need to learn calls and the play makers each know they have 5 front foot ball tackles to work towards their final play.
- The challenges in a Rugby season with travel etc. means that precious time needs to be spent at the front end of the season on technical things (scrum, line out, set plays)
- Each NRL team plays 24 games in the regular season, it means that combinations can be built as the season goes on (so a priority at being in peak physical condition), a super rugby season is in pro sports terms fairly short and sweet. In Super Rugby you have to hit the ground running with combinations from the start.
- Then other things like the length of the season for the top tier rugby player, etc. it all adds up to being vastly different from each other.
- The other thing is one sport has been pro for over 100yrs and another just over 20yrs. RL philosophies especially in Aus are entwined with a professional mentality, Union still at heart has many amateur characteristics and will build as a sport as time goes on