Why would he have a "lesser team" brought in for anything? The idea that Paul used a poor team contradicts his entire character. Here you have a guy consistently searching for the Pokemon he deems as strong, even so much as throwing out those he feels are weak. So why, on such a big occasion, would he suddenly use anything less (for the gym battle, or the match with Brandon)? And the very fact that they were brought in implies that they were reserves more than anything.
Paul relies more on type advantage than anything else. Almost all the members on that team had some move that were super-effective against ice-types. That's the same reason why he didn't bring Torterra. He obviously wasn't expecting to go up against Brandon when he selected the team and easily could have added some newbies to prove their strength.