You are absolutely kidding yourself if you think the premiers don’t have everyone else in the league gunning for them the very next year.
It’s quite obviously one of the key reasons that clubs find it so hard to go back to back.
To an extent. But it's also overstated.
The bottom four clubs can gun for them, be as motivated as they like......but they're still the bottom four clubs. If you're the reigning premier - take Brisbane this season, they're 99.99% certain to smash the bottom 4 teams at the Gabba no matter how motivated they are. A shit team gunning for you is still a shit team.
Good teams get the luxury of being able to win games when not at their best or playing particularly well. Every game is not up for grabs.