I wanted to see if BR was as bad as people say it was. I picked the KANTOOOOO rental pass and did the first arena and beat the first rank (there are 7 ranks to each arena, each tournament is 7 battles, it does take a while with all the unskippable animations). The first thing that dawned on me was that I was stuck with a Cut Ivysaur and a Rock Smash Wartortle for the rest of the game, leading me to believe I'd eventually hit a wall where I couldn't progress any further.
I didn't think that'd be the second rank tourney of the first arena when the last battler pulled out their final mon, a Rotom with Ominous Wind and some Electric attack. Your only resistance to Ghost is your first-route bird on either rental pass, then she would always get the stat boosts within three turns of sending it out. And none of your other mons can outspeed Rotom or hit it super effectively (except Charmeleon's Bite).
So now it's obvious that you need to create a custom pass and import your mons to see all the content the game has to offer. Which is... Trying to find the most cunny outfit to dress your female avatar in. That's it. You get no new mons (except the mystery gifts you have access to since boot up) or items, the ones you import gain no experience, and if your competent at teambuilding at all the first 6 ranks of the 10 or so arenas will be nothing but a chore. The online play (while it was still active) also had no rules or restrictions, and I'm not sure if it was even ranked or not.

tl;dr no reason to play this game. If you like gen 4 in 3D, play BDSP. If you like little girls, play any of the other title.